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。

请问这一题的解题思路

求问解题思路

求问解题思路

条件一：（30+⏹）（20+🔼）=864化简为20🔼-🔼^2=64 然后从2开始带入，得出当🔼=4时成立。条件二：⏹✖️🔼=24得出3、8和4、6两组可能解，分别带入，只有36和24成立，所以条件二充分。请问以上这个解题思路对吗，或者说有更简便的？

第14题 请徐老师解答 谢谢！

请问这道题的解题思路

第13题: 听老师jj课里讲的说选C，我不太明白条件2的分析，老师上课说条件2，若st同号，上式取等号，若st一正一负时，上式是小于号。那不就可以通过条件2直接判断上式大于号不成立吗，也就是答案是No。请老师更正下我的思路。

请徐老师讲下这两道题：这两个都做对了 但是感觉做的时候不太自信，想了一会，想听下老师的思路。谢谢老师！

麻烦徐老师讲一下Q9，选了E。我的思路是分析rounding后estimate的最大和最小的差值。

请徐老师讲一下Q7思路。读题是不是很明白题意说的到head的概率不是1/2。