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24个brand，对每个brand的四个方面进行评估，这四个方面是ABCD，评估结果有四种，excellent，good，not good，bad，至少有几个brand的两个方面either excellent or good？ （1）至少有10个brand的两个方面是excellent （2）至少有12个brand的三个方面是good

a/c是否小于1？ （1） a/（c-1）小于1 （2） （a-1）/c小于1

切线与圆

PS：总共66个学生，有18个是business major，24个是新生，还有36个什么也不是，我忘了最后是问，仅仅是新生不是business major 的还是仅仅是business major不是新生的？ 构筑答案：好像答案不是12 就是16.。。 解析： 18和24代表的韦恩图圈圈有重合，36代表的是自己单独的圈圈。 Total =66； 36个学生不在Business和Fresh 范畴里面，所以F+B=30; F 和B的共有学生=12， 是B不是F=6； 是F不是B=12。

PS：挺简单的，就是一个数轴吧-5到15都涂黑了，然后问哪个式子能代表？ |x-5|<10 这个不等式怎么解来着？忘了。。。变号问题

PS：讲一个租赁汽车的公司每一次购买会购买5辆新车，每次卖掉会卖掉3辆旧车，今年新增了14辆车，把每次买和每次卖都算做一次交易，问今年最少做了几次交易？

If it took Carol 1/2 hour to cycle from his house to the library yesterday, was the distance that he cycled greater then 6 miles? ( 1mile=5,280feet) (1) The average speed at which Carlos cycled from his house to the library yesterday was greater than 16 feet per second. (2) The average speed at which Carlos cycled from his house to the library yesterday was less than 18 feet per second

Of the 12 temporary employees in a certain company, 4 will be hired as permanent employees. If 5 of the 12 temporary employees are women, how many of the possible groups of 4 employees consist of 3 women and one man? A. 22 B. 35 C. 56 D. 70 E. 105

if x is positive, is x >3 1. (x-1)^2 >4 2. (x-2)^2 >9

if the average of the consecutive even integers a,b, and c is less than 13a, which of the following best describes the value of a? 答案： a is positive 为什么呢？