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.

请问这一题的解题思路

求问解题思路

求问解题思路

条件一：（30+⏹）（20+🔼）=864化简为20🔼-🔼^2=64 然后从2开始带入，得出当🔼=4时成立。条件二：⏹✖️🔼=24得出3、8和4、6两组可能解，分别带入，只有36和24成立，所以条件二充分。请问以上这个解题思路对吗，或者说有更简便的？

第14题 请徐老师解答 谢谢！

请问这道题的解题思路

第13题: 听老师jj课里讲的说选C，我不太明白条件2的分析，老师上课说条件2，若st同号，上式取等号，若st一正一负时，上式是小于号。那不就可以通过条件2直接判断上式大于号不成立吗，也就是答案是No。请老师更正下我的思路。

请徐老师讲下这两道题：这两个都做对了 但是感觉做的时候不太自信，想了一会，想听下老师的思路。谢谢老师！

麻烦徐老师讲一下Q9，选了E。我的思路是分析rounding后estimate的最大和最小的差值。

请徐老师讲一下Q7思路。读题是不是很明白题意说的到head的概率不是1/2。