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。

【请May老师回答】这题鸡精提供的答案是D 可是我觉得第二个条件不能得出呢 假设n三次方是x平方 除以n平方 是可以得到x/ n 平方 但是x/n 不一定是整数呀？

7.15/寂静：STUVW, 5个人， V和W中间必须隔一个人，求问共有几种组合？ 我的想法是这样的A（3,3）*A(2,2)*C(3,1)=36种；思路如下：先把V+C(3,1)+W看成一个整体；可得：A(2,2)*C(3,1)种排法；然后5个人可分成三类，于是A(3,3)。不知道我的想法对不对，请老师解答。感激不尽！

急求此题！谢谢老师！题目来7/6自寂静。x∈{1, 2, 3}，y∈{4,5,6}，z∈{7,8,9}，求yxx与z的乘积为偶数的概率？我根据求反可得：2/3x1/3x2/3=4/27 1-4/27=23/27 不等于5/9呀？我就是卡在这里了求教。谢谢！

请郭老师看一下这几题 谢谢老师

麻烦郭老师看一下这几题，谢谢老师

麻烦郭老师看一下这几题，谢谢

请郭老师帮我看一下这几道题，好几个都完全不会…

请郭老师帮我看一下这几道题，好几个都完全不会…

不是很明白为什么A选项不对 我觉得outnumber了给其他人写信的数量可以作为这个period Emily写信的结果出现 为什么不能用现在分词呢？