小安81篇3/63（XDF蓝书增补篇3）第3问求教

ffen

小安81篇3/63（XDF蓝书增补篇3）第三题，知道为什么选A了，但不知道如何排除其B D选项，也不知道自己这样排除C E是否正确，求解释……
原文第一段：No verysatisfactory account of the mechanism that caused the formation of the oceanbasins has yet been given. The traditional view supposes that the upper mantleof the earth behaves as a liquid when it is subjected to small forces for longperiods and that differences in temperature under oceans and continents aresufficient to produce convection in the mantle of the earth with risingconvection currents under the mid-ocean ridges and sinking currents under thecontinents. Theoretically, this convection would carry the continental platesalong as though they were on a conveyorbelt (conveyor belt: n. 传送带) andwould provide the forces needed to produce the split that occurs along theridge. This view may be correct: it has the advantage that the currents aredriven by temperature differences that themselves depend on the position of thecontinents. Such a back-coupling, in which the position of the moving plate hasan impact on the forces that move it, could produce complicated and varyingmotions.

3.     The author refers to a“conveyor belt” in line 13 in order to
(A) illustratethe effects of convection in the mantle
(B) show howtemperature differences depend on the positions of the continents
(C) demonstratethe linear nature of the Mid-Atlantic Ridge（M-A R在第二段中提到）
(D) describethe complicated motions made possible by back-coupling（A）
(E) account forthe rising currents under certain mid-ocean ridges（Rising currents由温差导致）

mofell

conveyor belt 传输带 表示了这2种变化之间的关系是什么紧密的，一个变化导致了另一个变化——with rising convection currents under the mid-ocean ridges and sinking currents under thecontinents.
所以选A illustratethe effects of convection in the mantle

wupenghui2000

convection是果，differences temperature是因，可排除E。
C和D都是在conveyor belt之后才出现，肯定错。
文中并未给出温度差的原因，B错。

小安81篇3/63（XDF蓝书增补篇3）第三题，知道为什么选A了，但不知道如何排除其B D选项，也不知道自己这样排除C E是否正确，求解释……
原文第一段：...
3.     The author refers to a“conveyor belt” in line 13 in order to
(A) illustratethe effects of convection in the mantle
(B) show howtemperature differences depend on the positions of the continents
(C) demonstratethe linear nature of the Mid-Atlantic Ridge（M-A R在第二段中提到）
(D) describethe complicated motions made possible by back-coupling（A）
(E) account forthe rising currents under certain mid-ocean ridges（Rising currents由温差导致）

-- by 会员 ffen (2011/1/27 14:28:46)

amy21mys

同楼上。以及补问，第六题为啥选B the upper mantle behaves a dense solid. 原文的tranditional view不是认为upper behaves as a liquid么？求解！跪谢！！

eyebabyemilywu

to amy21mys

第六题讲的是做后一段 explaining enclosed sea, .....except that the floor is overlaid by several kilometers of sediment. 最后举了black sea 的例子。所以选slowly settling foundation