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.

【请May老师回答】这题鸡精提供的答案是D 可是我觉得第二个条件不能得出呢 假设n三次方是x平方 除以n平方 是可以得到x/ n 平方 但是x/n 不一定是整数呀？

7.15/寂静：STUVW, 5个人， V和W中间必须隔一个人，求问共有几种组合？ 我的想法是这样的A（3,3）*A(2,2)*C(3,1)=36种；思路如下：先把V+C(3,1)+W看成一个整体；可得：A(2,2)*C(3,1)种排法；然后5个人可分成三类，于是A(3,3)。不知道我的想法对不对，请老师解答。感激不尽！

急求此题！谢谢老师！题目来7/6自寂静。x∈{1, 2, 3}，y∈{4,5,6}，z∈{7,8,9}，求yxx与z的乘积为偶数的概率？我根据求反可得：2/3x1/3x2/3=4/27 1-4/27=23/27 不等于5/9呀？我就是卡在这里了求教。谢谢！

请郭老师看一下这几题 谢谢老师

麻烦郭老师看一下这几题，谢谢老师

麻烦郭老师看一下这几题，谢谢

请郭老师帮我看一下这几道题，好几个都完全不会…

请郭老师帮我看一下这几道题，好几个都完全不会…

不是很明白为什么A选项不对 我觉得outnumber了给其他人写信的数量可以作为这个period Emily写信的结果出现 为什么不能用现在分词呢？