According to a theory advanced by researcher Paul Martin，the wave of species extinctions that occurred in North America about 11,000 years ago，at the end of the Pleistocene era，can be directly attributed to the arrival of humans，i.e.，the Paleoindians， who were ancestors of modern Native Americans. However，anthropologist Shepard Krech points out that large animal species vanished even in areas where there is no evidence to demonstrate that Paleoindians hunted them.Nor were extinctions confined to large animals： small animals，plants，and insects disappeared，presumably not all through human consumption. Krech also contradicts Martin's exclusion of climatic change as an explanation by asserting that widespread climatic change did indeed occur at the end of the Pleistocene. Still，Krech attributes secondary if not primary responsibility for the extinctions to the Paleoindians，arguing that humans have produced local extinctions elsewhere.But，according to historian Richard White，even the attribution of secondary responsibility may not be supported by the evidence. White observes that Martin's thesis depends on coinciding dates for the arrival of humans and the decline of large animal species，and Krech，though aware that the dates are controversial，does not challenge them；yet recent archaeological discoveries are providing evidence that the date of human arrival was much earlier than 11,000 years ago. 　3. In the last sentence of the passage， the author refers to “recent archaeological discoveries” (lines 27-30) most probably in order to 　　(A) Refute White's suggestion that neither Martin nor Krech adequately account for Paleoindians' contributions to the Pleistocene extinctions 　　(B) Cast doubt on the possibility that a more definitive theory regarding the causes of the Pleistocene extinctions may be forthcoming 　　(C) Suggest that Martin's， Krech's， and White's theories regarding the Pleistocene extinctions are all open to question 　　(D) Call attention to the most controversial aspect of all the current theories regarding the Pleistocene extinctions 　　(E) Provide support for White's questioning of both Martin's and Krech's positions regarding the role of Paleoindians in the Pleistocene extinctions 老师，我在做这道题的时候，首先定位到最后一句觉得没说什么重点，就有个yet转折，可能这是用来驳斥前面的某些观点的。所以看选项找有没有驳斥的意思的， 发现5个选项全都在驳斥。。。心里慌了往前找。再回去找的时候时间已到。我就随便选了个B（时间一到各种混乱），因为在做这篇文章之前，我大体看了下原文，记住了原文讲的是P反驳M，W反驳P。后来答案我也看明白了，我认为我做这道题的思路出现了偏差，我想问一下应该怎么修正。

这一题，主要区别在于by trying to与in trying to，为何in trying to好与 by呢？ 还有一个区别是划线最后的have had to与have themselves to之间的区别，为何这里不能用have themselves to呢？尤其是在划线前面已经出现了have themselves to的情况下？

没思路，不知道结合条件一及条件二如何得出X1的值...脑子不好使！

只能做到50的阶乘，乘以2的50次方，再加1 的结果 但是后面怎么思考就不清楚了，遇到这种题该如何去做，有什么直接的方法吗？

请May老师帮忙梳理一下这个题怎么用A排列或者C组合的方法算出答案，我每次遇到这种题似乎都有点毛病，不知道应该用A还是C还是结合...

条件一不是已经表明P是C的数量的两倍吗？而原文条件也说明了P或者C其中任意一个都可能为2/3的总量，而条件一表明P=2C 则总份额就是3C。C/（P+C）=1/3，可以得出答案啊，为什么不能选？

这题我认为主要考点在if与when的连用上以及consider后面接to be或者直接接noun。如果在BC选项it无指代可以排除，ADE三个选项中为何E是最优选项呢？这里情形我认为if和when都呢说得通，而且consider后面接noun或者to be在语法上没有问题。

这题正确选项E为什么which后面没有动词而是接的不定式形式，如果这样which后面就不是完整的句子了啊？

How many positive prime numbers are less than integer n? a) 14<n<20。 b) 13<n<17

这一题C，D两个选项中明显有一点不同就是一个用了but many scientist，一个用了and mant scientist. 从句意来看的话，这句话说了A提出了一个观点，但是很多科学家怀疑，然后转折P这个人之后测出来了。虽然D选项中P做的事情用过去时优于C选项中P用完成时，但我认为C选项连词用的比D好，为什么这题D选项优于C选项？