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。

DS：如果x和y是≥0的数，问3^xy次方是多少？ 条件1：5^x=11^y 条件2：3^x=9^y 请问这题答案是B吗？谢谢老师！

不明白这道题的总体积为什么是（x+2）(y+2)(z+2)而不是（x+1）(y+1)(z+1);厚度不是1吗？谢谢！

我觉得这题答案应该是A吧？∵105拆分质因数可得105=3*5*7（3个完全不同的质因数）∴x+y+z=15。怎么会是C呢？？？？

向May提问，我觉得这题情况会分得很复杂，想听下老师的思路？

想向May老师提问。这题我知道条件1单独成立，但对条件2没什么思路，只能想到穷举法，当p等于2*5,3*5,3*5,2*3,2*5,3*5时，m等于2*3,2*3,2*5,5,3,2，然后一个个除发现有的余数是1，有的余数大于1，条件2单独不成立。想问老师这个思路对吗？有没有更加简洁的思路？

不懂此题。已知有A,B,C和D共4个人；问：现在从这四个人中选出3人，是ACD的概率是多少？请详细解释，谢谢老师！

不理解第一个条件均值如何得出关于6倍数的结论，是连续7个数除7余数为5则为6的倍数，所以有一个6的倍数？

不理解第一个条件均值如何得出关于6倍数的结论，是连续7个数除7余数为5则为6的倍数，所以有一个6的倍数？

第8题的思路是以BC为底，从F向BC做垂线，跟BC交点H，FH为三角形FBC的高。然后三角形BFH跟三角形BDC相似，h：30=BF：BD，但是BF长度未知，望老师解答。

第8题的思路是以BC为底，从F向BC做垂线，跟BC交点H，FH为三角形FBC的高。然后三角形BFH跟三角形BDC相似，h：30=BF：BD，但是BF长度未知，望老师解答。