老师您好能否帮我讲解下下面这个文章考试时该如何读，我读完这种文章压根不知道在说什么，只知道在讲ocean basin形成机制的几种理论。No very satisfactory account of the mechanism that caused the formation of the ocean basins has yet been given. The traditional view supposes that the upper mantle of the earth behaves as a liquid when it is subjected to small forces for long periods and that differences in temperature under oceans and continents are sufficient to produce convection in the mantle of the earth with rising convection currents under the mid-ocean ridges and sinking currents under the continents. Theoretically, this convection would carry the continental plates along as though they were on a conveyor belt (conveyor belt: n. 传送带) and would provide the forces needed to produce the split that occurs along the ridge. This view may be correct: it has the advantage that the currents are driven by temperature differences that themselves depend on the position of the continents. Such a back-coupling, in which the position of the moving plate has an impact on the forces that move it, could produce complicated and varying motions. On the other hand, the theory is implausible because convection does not normally occur along lines, and it certainly does not occur along lines broken by frequent offsets (an abrupt bend in an object by which one part is turned aside out of line) or changes in direction, as the ridge is. Also it is difficult to see how the theory applies to the plate between the Mid-Atlantic Ridge and the ridge in the Indian Ocean. This plate is growing on both sides, and since there is no intermediate trench, the two ridges must be moving apart. It would be odd if the rising convection currents kept exact pace with them. An alternative theory is that the sinking part of the plate, which is denser than the hotter surrounding mantle, pulls the rest of the plate after it. Again it is difficult to see how this applies to the ridge in the South Atlantic, where neither the African nor the American plate has a sinking part. Another possibility is that the sinking plate cools the neighboring mantle and produces convection currents that move the plates. This last theory is attractive because it gives some hope of explaining the enclosed seas, such as the Sea of Japan. These seas have a typical oceanic floor, except that the floor is overlaid by several kilometers of sediment. Their floors have probably been sinking for long periods. It seems possible that a sinking current of cooled mantle material on the upper side of the plate might be the cause of such deep basins. The enclosed seas are an important feature of the earth’s surface, and seriously require explanation because, in addition to the enclosed seas that are developing at present behind island arcs, there are a number of older ones of possibly similar origin, such as the Gulf of Mexico, the Black Sea, and perhaps the North Sea.

第8题的思路是以BC为底，从F向BC做垂线，跟BC交点H，FH为三角形FBC的高。然后三角形BFH跟三角形BDC相似，h：30=BF：BD，但是BF长度未知，望老师解答。

求问此题：DS：一个矩形地毯问面积是否大于160？ 条件1：对角线>21 条件2：至少有一条边大于8 谢谢！

求问此题的详细解法。谢谢老师~！

下面那个圆的半径我求不出来。请老师答疑！谢谢！

请问这道题是选E吗（答案我给忘了）？一个数N是否能被4！的三次方整除 1）这个数能被6！的二次方整除 2）这个数能被9！整除

5^500 + 5^501 + 5^502 + 5^503 最大的质因子是多少？求具体解法！谢谢老师！

求问此题：一个正方体，选三条不在同一顶点的棱涂成红色，问有几种方法？我的计算过程是C(12,1)*C(7,1)*C(2,1)=168.不知道思路正确与否，请老师答疑解惑。谢谢！

此题求解：DS：3个数，问中位数是否大于平均数？ 条件1：最大数和最小数之和大于中位数； 条件2：最大数=450+平均数，最小数=平均数-150 谢谢！

一个正方体，选三条不在同一顶点的棱涂成q红色，问有几种方法？ 请may回答 我算的是（ C3 12 ）-8