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easttiger2010

Scientists generally credit

violent collisions between

tectonic plates, the mobile

Line
fragments of Earth’s rocky
(5)outer shell, with sculpting
the planet’s surface, as, for
example, when what is now
the Indian subcontinent col-
lidedwith Asia
, producing
(10)the
Himalayan
   Mountains.
However, plate tectonics
cannot fully explain certain
massive surface features,
such as the “superswell”
(15)of southern
Africa, a vast
plateau over 1,000 miles
across and nearly a mile
high.Geologic evidence





shows that southern African





(20)has been slowly rising for





the past 100 million years,





yet it has not experienced





a tectonic collision for





nearly 400 million years.





(25)The explanation may be in





Earth’s mantle, the layer of





rock underlying the tectonic





plates and extending down





over 1,800 miles to the outer





(30)edge of Earth’s iron core.





Since the early twentieth





century, geophysicists have





understood that the mantle





churns and roils like a thick





(35)soup.The relative low





density of the hottest rock





makes that material buoyant,





so it slowly ascends, while





cooler, denser rock sinks





(40)until heat escaping the mol-





ten core warms it enough to





make it rise again.While





this process of convection





was known to enable the





(45)horizontal movement of tec-





tonic plates, until recently





geophysicists were skeptical





of its ability to lift or lower the





planet’s surface vertically.





(50)However, recent technolog-





ical advances have allowed





geophysicists to make three-





dimensional “snapshots”





of the mantle by measuring





(55)vibrations, or seismic waves,





set in motion by earthquakes





originating in the planet’s





outer shell and recording





the time it takes for them to





(60)travel from an earthquake’s





epicenter to a particular





recording station at the





surface.Because geo-





physicists know that seismic





(65)waves become sluggish in





hot, low-density rock, and





speed up in colder, denser





regions, they can now infer





the temperatures and den-





(70)sities in a given segment of





the interior.By compiling





a map of seismic velocities





from thousands of earth-





quakes across the globe,





(75)they can also begin to map





temperatures and densities





throughout the mantle.These





methods have revealed some





unexpectedly immense for-





(80)mations in the deepest parts





of the mantle; the largest





of these is a buoyant mass





of hot rock directly below






Africa’s southern tip.Dis-




(85)pelling researchers’ initial





doubts, computer models





have confirmed that this





formation is buoyant enough





to rise slowly within the mantle





(90)and strong enough to push






Africa upward as it rises. ---------------------------------------


Q25:

In line 10, the author mentions the Himalayan Mountains most likely in order to

A.highlight certain similarities between the southern African superswell and other massive features on Earth’s surface

B.identify a feature of Earth’s surface that predates the origins of the southern African superswell

C.provide an example of a feature of Earth’s surface that can explained by plate tectonics

D.suggest that geophysicists are correct in attributing the sculpting of Earth’s surface to violent collisions between tectonic plates

E.give an example of a feature of Earth’s surface that scientists are unable to explain fully

---------------------------
答案是C，我觉得D和原文定位（蓝色高亮部分）更贴切。

请哪位高人指点，谢谢！

---------------------------------------


Q25:

In line 10, the author mentions the Himalayan Mountains most likely in order to

A.highlight certain similarities between the southern African superswell and other massive features on Earth’s surface

B.identify a feature of Earth’s surface that predates the origins of the southern African superswell

C.provide an example of a feature of Earth’s surface that can explained by plate tectonics

D.suggest that geophysicists are correct in attributing the sculpting of Earth’s surface to violent collisions between tectonic plates

E.give an example of a feature of Earth’s surface that scientists are unable to explain fully

---------------------------
答案是C，我觉得D和原文定位（蓝色高亮部分）更贴切。

请哪位高人指点，谢谢！

easttiger2010

up下，呼唤NN来看看！

easttiger2010

up 一下！