og14讨论

Venus

我基本没看懂但错一个，大家是这样吗？
科技文章我常常这样，你们呢？

Venus

A meteor stream is composed of dust particles that have been ejected from a parent comet at a variety of velocities. These particles follow the same orbit as the parent comet, but due to their differeing velocities they slowly gain on or fall behind the disintegrating comet until a shroud of dust surrounds the entire cometary orbit.
Astronomers have hypothesized that a meteor stream should broaden with time as the dust particles’ individual orbits are perturbed by planetary gravitational fields. A recent computer-modeling experimetn tested this hypothesis by tracking the influence of planetary gravitation over a projected 5,000-year period on the positions of a group of hypothetical dust particles. In the model, the particles were randomly distributed throughout a computer simulation of the orbit of an actual meteor stream, the Geminid. The researcher found, as expected,
that the computer-model stream broadened with time. Coventional theories, however, predicted that the distribution of particles would be increaingly dense toward the center of a meteor stream. Surpringly, the computer-model meteor stream gradually came to resemble a thick-walled, hollow pipe.
Whenever the Earth passes through a meteor stream, a meteor shower occurs. Moving at a little over 1,500,000 miles per day around its orbit, the Earth would take, on average, just over a day to cross the hollow, computer-model Geminid stream if the stream were 5,000 years old. Two brief periods of peak meteor activity during the shower would be observed, one as the Earth entered the thick-walled “pipe” and one as it exited.
There is no reason why the Earth should always pass through the stream’s exact center, so the time interval between the two bursts of activity would vary from one year to the next.
Has the predicted twin-peaked activity been observed for the actual yearly GEminid meteor shower? The Geminid data between 1970 and 1979 show just such a bifurcation, a secondary burst of meteor activity being clearly visible at an average of 19 hourse (1,200,000 miles) after the first burst. The time intervals between the bursts suggest the actual Geminid stream is about 3,000 years old.

80. The primary focus of the passage is on which of the following?
(A) Comparing two scientific theories and contrasting the predictions that each would make concerning a natural phenomenon
(B) Describing a new theoretical model and noting that it explains the nature of observations made of a particular natural phenomenon
(C) Evaluating the results of a particular scientific experiment and suggesting further areas for research
(D) Explaining how two different natural phenomena are related and demonstrating a way to measure them
(E) Analyzing recent data derived from observations of an actual phenomenon and constructing a model to explain the data

81. According to the passage, which of the following is an accurate statement concerning meteor streams?
(A) Meteor streams and comets start out with smiliar orbits, but only those of meteor streams are perturbed by planetary gravittion.
(B) Meteor streams grow as dust particles are attracted by the gravitational fields of comets.
(C) Meteor streams are composed of dust particles derived from comets.
(D) Comets may be composed of several kinds of materials, while meteor streams consitst only of large dust particles.
(E) Once formed, meteor streams hasten the further disintegration of comets.

82. The author states that the research described in the first paragraph was undertaken in order to
(A) determine the age of an actual meteor stream
(B) Identify the various structural features of meteor streams
(C) explore the nature of a particularly interesting meteor stream
(D) test the hypothesis that meteor streams become broader as they age
(E) show that a computer model could help in explaining actual astronomical data

83. It can be inferred from the passage that which of the following would most probably be observed during the Earth’s passage through a meteor stream if the conventional theories mentioned in line 18 were
(A) Meteor activity would gradually increase to a single, intense peak, and then gradually decline.
(B) Meteor activity would be steady throughout the period of the meteor shower.
(C) Meteor activity would rise to a peak at the beginning and at the end of the meteor shower.
(D) Random bursts of very high meteor activity would be interspersed with periods of very little activity.
(E) In years in which the Earth passed through only the outer areas of a meteor stream, meteor activity would be absent.

84. According to the passage, why do the dust particles in a meteor stream eventually surround a comet’s orginla orbit?
(A) They are ejected by the comet at differing velocities.
(B) Their orbits are uncontrolled by planetary gravitational fields.
(C) They become part of the meteor stream at different times.
(D) Their velocity slows over time.
(E) Their ejection velocity is slower than that of the comet.

85. The passage suggests that which of the following is a prediction concerning meteor streams that can be derived from both the conventional theories mentioned in line 18 and the new computer-derived theory?
(A) Dust particles in a meteor stream will usually be distributed evenly throughout any cross section of the steam.
(B) The orbits of most meteor streams should cross the orbit of the Earth at some point and give rise to a meteor shower.
(C) Over time the distribution of dust in a meteor stream will usually become denser at the outside edges of the stream than at the center.
(D) Meteor showers caused by older by older meteor streams should be, on average, longer in duration than those caused by very young meteor streams.
(E) The individual dust particles in older meteor streams should be, on average, smaller than those that compose younger meteor streams.

86. It can be inferred from the last paragraph of the passage that which of the following must be true of the Earth as it orbits the Sun?
(A) Most meteor streams it encounters are more than 2,000 years old.
(B) When passing through a meteor stream, it usually passes near to the stream’s center.
(C) It crosses the Geminid meteor stream once every year.
(D) It usually takes over a day to cross the actual Geminid meteor stream.
(E) It accounts of msot of the gravitaitonal perturbation affecting the Geminid meteor stream.

87. Which of the following is an assumption underlying the last sentence of the passage?
(A) In each of the years between 1970 and 1979, the Earth took exactly 19 hours to cross the Geminid meteor stream.
(B) The comet associated with the Geminid meteor stream has totally disintegrated.
(C) The Geminid meteor stream should continue to exist for at least 5,000 years.
(D) The Geminid meteor stream has not broadended as rapidly as the conventiona ltheories would have predicted.
(E) The computer-model Geminid meteor stream provides an accurate representation of the development of the actual Geminid stream.

anchoret

错的那个想通了吗？如果没想通的话是哪一个？

Venus

我只是觉得科技文章我很难读懂，定位也困难，只是凭感觉选。对于这个情况没有对策？
你说怎么办？
上了考场这种感觉一定会毁了其他的题目。

bon

这篇文章的85题不是很懂，麻烦大牛解释一下

fair_sword

85题OG解释的很清，你先仔细看，如果还不行，在回来问，这样对你更有用

sheila123

我觉得OG的解释不是很好，题干是要找二者的共同点，在第一段的倒数第二句话：Conventional theories,however, pridicted that that the distribution of particles would be increasingly dense toward the center of a meteor stream.那不就是说随着时间的增加stream 应该越来越密集紧缩，所以越老的stream 所造成的meteor shower 的duration 应该越短才是呀。

另外，OG在解释中将Astronomers have hypothesized............的扩散理论认为是传统理论，同时又用上句however 明确指出传统理论预测会收紧，把本来挺明确的结构关系搞乱，请牛牛们解释一下第一段的结构，谢谢。

醋醋妹妹

题85的两个理论的共同点: Astronomers have hypothesized that a meteor stream should broaden with time 和In the model... The researcher found, as expected,that the computer-model stream broadened with time. 都是指随着时间增长, stream越来越宽. 所以老的stream比小的宽大, 从而导致所产生的shower老的比小的时间长. (这个shower是地球穿越这个stream而引起的).

第一段:

A meteor stream is composed of dust particles that have been ejected from a parent comet at a variety of velocities. These particles follow the same orbit as the parent comet, but due to their differeing velocities they slowly gain on or fall behind the disintegrating comet until a shroud of dust surrounds the entire cometary orbit. 介绍了meteor stream是怎么回事

Astronomers have hypothesized that a meteor stream should broaden with time as the dust particles’ individual orbits are perturbed by planetary gravitational fields./// A recent computer-modeling experimetn tested this hypothesis by tracking the influence of planetary gravitation over a projected 5,000-year period on the positions of a group of hypothetical dust particles. In the model, the particles were randomly distributed throughout a computer simulation of the orbit of an actual meteor stream, the Geminid. The researcher found, as expected,
that the computer-model stream broadened with time. 原来(传统)的观点---stream越变越宽. 实验证明的确如此.

Coventional theories, however, predicted that the distribution of particles would be increaingly dense toward the center of a meteor stream. ///Surpringly, the computer-model meteor stream gradually came to resemble a thick-walled, hollow pipe. 传统观念人为粒子象中心聚集, 但实验发现粒子呈管壮分布.

fair_sword

OG在解释中将Astronomers have hypothesized............的扩散理论认为是传统理论，同时又用上句however 明确指出传统理论预测会收紧，把本来挺明确的结构关系搞乱，请牛牛们解释一下第一段的结构，谢谢。

5个同学排成排。23，1，45， 这是中间细，两头dense的排法，23与1间隔2米。试验结果是这样。

conventional theories. 2，314，5， 中间dense,. 2与314间隔2米。

虽着时间older. 间隔变大....， 妹妹明白了吗。这个地方比较难讲。我想了好长时间

tony6

谢谢FAIRSWORD，顿开茅塞。不过，这篇文章真考时肯定做不出的，在10分钟多一点的时间里。