4月语文JJ太太乐wjy_slq(佳佳)RC49CR100.更新停止

wjy_slq

以下是引用TINTINGER在2009-4-12 20:11:00的发言：
给楼主加油

谢谢~~~

wjy_slq

祝福明天考试的人都有好成绩· 大家晚安。

goushichou

谢谢佳佳妹妹,给你加油, 祝福你!!

songlovegt

http://www.britannica.com/EBchecked/topic/625665/Venus

Venus

Character of the surface » Surface composition

A number of the Soviet landers carried instruments to analyze the chemical composition of the surface materials of Venus. Because only the relative proportions of a few elements were measured, no definitive information exists concerning the rock types or minerals present. Two techniques were used to measure the abundances of various elements. Gamma-ray spectrometers, which were carried on Veneras 8, 9, and 10 and the landers of the Soviet Vega 1 and 2 missions, measured the concentrations of naturally radioactive isotopes of the elements uranium, potassium, and thorium. X-ray fluorescence instruments, carried on Veneras 13 and 14 and Vega 2, measured the concentrations of a number of major elements.

The Venera 8 site gave indications that the rock composition may be similar to that of granite or other igneous rocks that compose Earth’s continents. This inference, however, was based only on rather uncertain measurements of the concentrations of a few radioactive elements. Measurements of radioactive elements at the Venera 9 and 10 and Vega 1 and 2 landing sites suggested that the compositions there resemble those of basalt rocks found on Earth’s ocean floors and in some volcanic regions such as Hawaii and Iceland. The Venera 13 and 14 and Vega 2 X-ray instruments measured concentrations of silicon, aluminum, magnesium, iron, calcium, potassium, titanium, manganese, and sulfur. Although some differences in composition were seen among the three sites, on the whole the elemental compositions measured by all three landers were similar to those of basalts on Earth.

A surprising result of orbital radar observations of Venus is that the highest elevations on the planet exhibit anomalously high radar reflectivity. The best interpretation seems to be that the highest elevations are coated with a thin layer of some semiconducting material. Its composition is unknown, but it could be an iron-containing mineral such as pyrite or magnetite, which formed at cooler, higher elevations from low concentrations of atmospheric iron(II) chloride vapour in the atmosphere.

Character of the surface » Surface features

Earth-based observatories and Venus-orbiting spacecraft have provided global-scale information on the nature of the planet’s surface. All have used radar systems to penetrate the thick Venusian clouds.

The entire surface of the planet is dry and rocky. Because there is no sea level in the literal sense, elevation is commonly expressed as a planetary radius—i.e., as the distance from the centre of the planet to the surface at a given location. Another method, in which elevation is expressed as the distance above or below the planet’s mean radius, is also used. Most of the planet consists of gently rolling plains. In some areas the elevations change by only a few hundred metres over distances of hundreds of kilometres. Globally, more than 80 percent of the surface deviates less than 1 km (0.6 mile) from the mean radius. At several locations on the plains are broad, gently sloping topographic depressions, or lowlands, that may reach several thousand kilometres across; they include Atalanta Planitia, Guinevere Planitia, and Lavinia Planitia.

Two striking features are the continent-sized highland areas, or terrae—Ishtar Terra in the northern hemisphere and Aphrodite Terra along the equator. Ishtar is roughly the size of Australia, while Aphrodite is comparable in area to South America. Ishtar possesses the most spectacular topography on Venus. Much of its interior is a high plateau, called Lakshmi Planum, that resembles in configuration the Plateau of Tibet on Earth. Lakshmi is bounded by mountains on most sides, the largest range being the enormous Maxwell Montes on the east. These mountains soar about 11 km (7 miles) above the mean radius of Venus. The topography of Aphrodite, more complex than that of Ishtar, is characterized by a number of distinct mountain ranges and several deep, narrow troughs. In addition to the two main terrae are several smaller elevated regions, including Alpha Regio, Beta Regio, and Phoebe Regio.

Many of the surface features on Venus can be attributed to tectonic activity—that is, to deformational motions within the crust. These include mountain belts, plains deformation belts, rifts, coronae, and tesserae, which are discussed in turn below (see also
                    tectonic landform).

Character of the surface » Surface features » Mountain belts
            

Found in the terrae, Venus’s mountain belts are in some ways similar to ones on Earth such as the Himalayas of Asia and the Andes of South America. Among the best examples are those that encircle Lakshmi Planum, which in addition to Maxwell Montes include Freyja, Akna, and Danu Montes. Maxwell Montes is particularly broad and comparable in size to the Himalayas.

Venus’s mountain belts typically consist of parallel ridges and troughs with spacings of 5–10 km (3–6 miles). They probably developed when broad bands of the lithosphere were compressed from the sides and became thickened, folding and thrusting surface materials upward. Their formation in some respects thus resembles the building of many mountain ranges on Earth. On the other hand, because of the lack of liquid water or ice on Venus, their appearance differs in major ways from their counterparts on Earth. Without the flow of rivers or glaciers to wear them down, Venusian mountain belts have acquired steep slopes as a result of folding and faulting. In some places the slopes have become so steep that they have collapsed under their own weight. The erosional forms common in mountainous regions on Earth are absent.

Character of the surface » Surface features » Plains deformation belts

Although plains deformation belts are similar in some ways to mountain belts, they display less pronounced relief and are found primarily in low-lying areas of the planet, such as Lavinia Planitia and Atalanta Planitia. Like mountain belts, they show strong evidence for parallel folding and faulting and may form primarily by compression, deformation, and uplift of the lithosphere. Within a given lowland, it is common for deformation belts to lie roughly parallel to one another, spaced typically several hundred kilometres apart.

Character of the surface » Surface features » Rifts
            

Rifts (see
                    rift valley) are among the most spectacular tectonic features on Venus. The best-developed rifts are found atop broad, raised areas such as Beta Regio, sometimes radiating outward from their centres like the spokes of a giant wheel. Beta and several other similar regions on Venus appear to be places where large areas of the lithosphere have been forced upward from below, splitting the surface to form great rift valleys. The rifts are composed of innumerable faults, and their floors typically lie 1–2 km (0.6–1.2 miles) below the surrounding terrain. In many ways the rifts on Venus are similar to great rifts elsewhere, such as the East African Rift on Earth or Valles Marineris on Mars; volcanic eruptions, for example, appear to have been associated with all these features. The Venusian rifts differ from Earth and Martian ones, however, in that little erosion has taken place within them owing to the lack of water.

Character of the surface » Surface features » Coronae
            

Coronae (Latin: “garlands” or “crowns”) are landforms that apparently owe their origin to the effects of hot, buoyant blobs of material, known from terrestrial geology as diapirs, that originate deep beneath the surface of Venus. Coronae evolve through several stages. As diapirs first rise through the planet’s interior and approach the surface, they can lift the rocks above them, fracturing the surface in a radial pattern. This results in a distinctive starburst of faults and fractures, often lying atop a broad, gently sloping topographic rise. (Such features are sometimes called novae, a name given to them when their evolutionary relationship to coronae was less certain.) Once a diapir has neared the surface and cooled, it loses its buoyancy. The initially raised crust then can sag under its own weight, developing concentric faults as it does so. The result is a circular-to-oval pattern of faults, fractures, and ridges. Volcanism can occur through all stages of corona formation. During the late stages it tends to obscure the radial faulting that is characteristic of the early stages.

Coronae are typically a few hundred kilometres in diameter. Although they may have a raised outer rim, many coronae sag noticeably in their interiors and also outside their rims. Hundreds of coronae are found on Venus, observed at all stages of development. The radially fractured domes of the early stages are comparatively uncommon, while the concentric scars characteristic of mature coronae are among the most numerous large tectonic features on the planet.

Character of the surface » Surface features » Tesserae
            

Tesserae (Latin: “mosaic tiles”) are the most geologically complex regions seen on Venus. Several large elevated regions, such as Alpha Regio, are composed largely of tessera terrain. Such terrain appears extraordinarily rugged and highly deformed in radar images, and in some instances it displays several different trends of parallel ridges and troughs that cut across one another at a wide range of angles. The deformation in tessera terrain can be so complex that sometimes it is difficult to determine what kinds of stresses in the lithosphere were responsible for forming it. In fact, probably no single process can explain all tessera formation. Tesserae typically appear very bright in radar images, which suggests an extremely rough and blocky surface at scales of metres. Some tesserae may be old terrain that has been subjected to more episodes of mountain building and faulting than have the materials around it, each one superimposed on its predecessor to produce the complex pattern observed.

Character of the surface » Surface features » Volcanic features

Along with intense tectonic activity, Venus has undergone much volcanism. The largest volcanic outpourings are the huge lava fields that cover most of the rolling plains. These are similar in many respects to fields of overlapping lava flows seen on other planets, including Earth, but they are far more extensive. Individual flows are for the most part long and thin, which indicates that the erupting lavas were very fluid and hence were able to flow long distances over gentle slopes. Lavas on Earth and the Moon that flow this readily typically consist of basalts, and so it is probable that basalts are common on the plains of Venus as well.

Of the many types of lava-flow features seen on the Venusian plains, none are more remarkable than the long, sinuous canali. These meandering channels usually have remarkably constant widths, which can be as much as 3 km (2 miles). They commonly extend as far as 500 km (300 miles) across the surface; one is 6,800 km (4,200 miles) long. Canali probably were carved by very low-viscosity lavas that erupted at sustained high rates of discharge. In a few instances segments of canali appear to proceed uphill, which suggests that crustal deformation took place after the channels were carved and reversed the gentle downward surface slopes to upward ones. Other channel-like volcanic features on Venus include sinuous rilles that may be collapsed lava tubes (see
                    lava), and large, complex compound valleys that apparently result from particularly massive outpourings of lava.

In many locations on Venus, volcanic eruptions have built edifices similar to the great volcanoes of Hawaii on Earth or those associated with the Tharsis region on Mars. Sif Mons is an example of such a volcano; there are more than 100 others distributed widely over the planet. Known as shield volcanoes, they reach heights of several kilometres above the surrounding plains and can be hundreds of kilometres across at their base. They are made up of many individual lava flows piled on one another in a radial pattern. They develop when a source of lava below the surface remains fixed and active at one location long enough to allow the volcanic materials it extrudes to accumulate above it in large quantities. Like those found on the rolling plains, the flows constituting the shield volcanoes are generally very long and thin and are probably composed of basalt.

When a subsurface source of lava is drained of its contents, the ground above it may collapse, forming a depression called a caldera. Many volcanic calderas are observed on Venus, both atop shield volcanoes and on the widespread lava plains. They are often roughly circular in shape and overall are similar to calderas observed on Earth and Mars. The summit region of Sif Mons, for example, exhibits a caldera-like feature 40–50 km (25–30 miles) in diameter.

Along with the extensive lava plains and the massive shield volcanoes are many smaller volcanic landforms. Enormous numbers of small volcanic cones are distributed throughout the plains. Particularly unusual in appearance are so-called pancake domes, which are typically a few tens of kilometres in diameter and about 1 km (0.6 mile) high and are remarkably circular in shape. Flat-topped and steep-sided, they appear to have formed when a mass of thick lava was extruded from a central vent and spread outward for a short distance in all directions before solidifying. The lavas that formed such domes clearly were much more viscous than most lavas on Venus. Their composition is unknown, but—given the knowledge of lavas on Earth—they are likely to be much richer in silica (see
                    silica mineral) than the basalts thought to predominate elsewhere on the planet.

Volcanic edifices are not uniformly distributed on Venus. Although they are common everywhere, they are particularly concentrated in the Beta-Atla-Themis region, between longitudes 180° and 300° E. This concentration may be the consequence of a broad active upwelling of the Venusian mantle in this area, which has led to enhanced heat flow and formation of magma reservoirs.

songlovegt

发重了

[此贴子已经被作者于2009-4-13 5:15:49编辑过]

loveroddick

我怎么觉得CR16是数学jj，在数学那边见过……

hoyoto

可能加错了吧

hoyoto

补个 SC JJ 第6道原题
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（1）    GWD-26-Q20

    

In 1981 children
in the United States
spent an average of slightly less than two and a half hours a week doing
household chores; by 1997 they had spent nearly six hours a week.

    

A.    chores; by 1997 they had spent nearly six
hours a week

    

B.     chores; by 1997 that figure had grown to
nearly six hours a week

    

C.     chores, whereas nearly six hours a week
were spent in 1997

    

D.    chores, compared with a figure of nearly
six hours a week in 1997

    

E.     chores, that figure growing to nearly six
hours a week in 1997

    

 

    

 

    

B
the best  A中的they没有指代对象，不能指代1981年的children。 

    

mastmyy

好人，加油！

wjy_slq

以下是引用songlovegt在2009-4-13 3:25:00的发言：
发重了

呵呵  谢谢你这么热心。