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.

有三组滑冰运动员，第一组全是single women，6个人，第二组是paired，3组，第三组是single men，5个人，他们的出场顺序是single women-paired-single men，问一共有多少种order？ （1）6+3+5 （2）6！*3！*5！ （3）6*3*5 （4）（6+3+5）！

一个数能被10^r 整除，不能被10^（r+1）整除，求r？ （1）这个数能被2^5整除，不能被2^6整除 （2）这个数能被5^6整除，不能被5^7整除

30个蓝球10个红球，摸一个放回去再摸一个，摸到两个颜色一样的就结束。第一个摸的是红球，问在摸到两个蓝球前摸到红球的概率是多少。

两个整数XY，问是否知道XY的值？ （1）X,Y的common divisor是（一个值） （2）X/Y=（一个值）

一个rectangular block，求表面积？ （1）each two面的面积是11，其中一边长（某个数） （2）一个边的边长是（某个数）

PS：俩骰子每面各是1-6，且每投一次各个数字冲上的概率一致。问同时扔这俩，俩加和是9或者5的概率？选了2/9。 老师您好，解析给是：共有6*6=36种，等于9的情况3+6,4+5,5+4,6+3。等于5的情况1+4,2+3,3+2,4+1。一共8个，所以是8/36=2/9。这是考虑了顺序的，8种情况是考虑到顺序，但我觉得不应该考虑顺序，应该只有4种。请指点。

一道数学机经题，没有具体数字麻烦老师讲下思路~~谢谢~~ DS： 有10个马拉松运动员平均成绩是2分32秒，问能否推出range？ 条件1：最快5个的range是XX 条件2：最慢5个的range是XX 构筑：不确定，选了e 构筑答案：E 整理菌答案：详见解析 解析: 整理菌列了几组数字来计算，感觉不能推出E。 但应该可以根据平均成绩以及人数，进行系统的计算。欢迎讨论！！

还是数学机经题~想问一下老师这个题不用反证法可以解吗？？或者反证法合理吗？？谢谢~~ DS：问h是不是prime number 条件1：h的factor都大于根号h 条件2：h的factor都大于h/2 反证法： 假设h = a*b 且a, b >1， h不是质数。 条件1： a，b>根号h，then H > 根号h*根号h = h， 推出矛盾，所以h不能写成两个大于1的数相乘，所以h是质数； 条件2： 同理 H>2/h*2/h=h^2/4 推出h<4, then h = 2 or 3, 是质数， 与假设矛盾。所以h是质数。 选D

有一个矩形的green sport field，长为L，宽为W，周围是一圈walking trace，宽为d，其中四个角是矩形的，面积分别为半径为d的圆形的4分之1，求walking trace的面积 条件1：矩形周长是36 条件2：d=20

平行四边形边长为6，面积为18，求角度可能是以下哪个？ 30 45 60 90 120