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.

@Tina老师，老师，这道题帮忙讲一下b和c选项呗。主要区别在谓语单复数和后面的to provide 还是providing。主语是两个不可数名词and并列，谓语要用复数么？

@陆旭老师 我想问一下 这里面的数字7是哪里来的呀？我想了一下排除0和它本身应该还有8个呀，不是很明白。

@陆旭老师 为什么这道题选b呀？我把（1）代进去能求出答案，把（2）代入则x=5与题目要求不符，求讲解。谢谢

@陆旭老师 这道题思路是什么呀？应该怎么做呢？

这道数学题 我想问问数学老师为什么我的两个方法答案都不对 首先 我理解这道题是问事件M或者R只发生一个的概率 我的第一个方法就是用M发生*R不发生+M不发生*R发生 这样哪里出错了 需要怎么改呢？ 我的第二个方法是用总体减去M和R同时发生的概率再减去M和R都不发生的概率，这里哪里出错了 要怎么改呢？ 谢谢老师的回答！

@英吉老师 我想问一下这道题A选项错在了哪里，算是犯了什么错误？

@英吉老师 这一道题里的c选项还是不是很明白哪里错了，请问这句话要是怎么改就算对了呢？

@徐小梅老师，徐老师您好，第4)题，我也看到了“至少2人”这个字眼，也是按照至少2人来算的。但我是这么理解的：原来男女共有12个人，先从5个女生中取2个人，保证了至少有两个女生，所以是C5^2; 接着，再让剩下的3个女生和7个男生合并，共10人，取3个人（此时不论男女都可以），是C10^3。然后合起来就是C5^2*C10^3。

为什么4）不能直接用C5^2 *C10^3?先从5个女生中选2人，再从剩下的10人中选3。这样我算出来的是1200。但是按照图片上老师的方法算的是596。很疑惑，求老师解答一下，谢谢！

为什么分子是5 就一定有一个分母是2的三次方有一个分子是1呢？