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。

讲解

DS：已知9个数的平均数是43，求标准方差 1）最小的那个数是43 2）最大的那个数是43

一个数n的因子有2，3，5，n < 200，求n？ 条件1：4不是他的因子 条件2：9是他的因子

一辆火车走600 miles的路程，一般需要10h；火车中间走了一段速度20 miles的路；接下来是速度60miles的路，问速度60miles走了多久？ 条件1：速度20 miles走了3个小时 条件2：600 miles路程平均速度为56miles

一个数被10r整除，但不被10r+1整除，求r？ 条件1：这个数被25整除不被26整除 条件2：这个数被56整除不被57整除

数学考了一道，本来某一天下午两点水池剩n方水，每小时漏1/4方，每天下午一点会加进去14方，问水池剩m方的时候是星期几几点？

一个长方形长x宽y，能不能比较沿x边卷起的圆柱体体积和y边卷起圆柱体的体积？ 条件1：2x大于y 条件2：x小于3y

一个公司准备给一个地区中大于等于65，并且在当地呆的时间小于等于5年的人，发放谋谋福利，问这部分所占比例？ 条件1：该地区≥65岁的占比（某个值） 条件2：该地区呆的时间≤5年的人占比（某个值）

问x^y是否是odd？ 条件1：x是odd 条件2：可以求出来y是odd

编号1-8的蓝木板放到一个箱子里，编号1-8的红木板放到另一个。每个箱子各抽一块板，问抽到蓝木板和红木板编号一样的几率是多少？ 老师为什么不是 1/64?