陆旭老师，我有一些做过的assumption题目取非的句子搞不清，你能帮忙看下吗(不说这道题目的解题思路，单纯就是取非问题，特别是双重否定或者从句里面有否定词） 1.No part of a person’s brain that is damaged by a stroke ever recovers.---> some part of a person's brain that is damaged by a stroke ever recovers. 2.Impairment of linguistic capabilities does not occur in people who have not suffered any damage to any language center of the brain.这个句子我不太会取非，正过来说这个句子就是Impairment of linguistic capabilities occurs in people who have suffered any damage to any language center of the brain.那么我取非是Impairment of linguistic capabilities occurs in people who have not suffered any damage to any language center of the brain. 3.If there are language centers on the left side of the brain, any serious stroke affecting that side of the brain damages at least one of them. 取非If there are language centers on the left side of the brain, any serious stroke affecting that side of the brain damages nothing of them. 4.这题出现两个not The collection fee will not significantly affect the purchasing power of most residents, even if their households do not reduce the amount of trash they put out. 我取非直接去前面的not: The collection fee will significantly affect the purchasing power of most residents, even if their households do not reduce the amount of trash they put out. 5.这个也差不多 Not all steel producers were unaffected by country A’s newly imposed tariffs. 我取非All steel producers were unaffected bycountry A’s newly imposed tariffs. 6.There are no plants native to western Africa that, if domesticated, could serve as staple food crops. 这个if domesticated是不是可以不管，直接改成There are some plants native to western Africa that, if domesticated, could serve as staple food crops.

@Tina老师，老师，这道题帮忙讲一下b和c选项呗。主要区别在谓语单复数和后面的to provide 还是providing。主语是两个不可数名词and并列，谓语要用复数么？

@陆旭老师 我想问一下 这里面的数字7是哪里来的呀？我想了一下排除0和它本身应该还有8个呀，不是很明白。

@陆旭老师 为什么这道题选b呀？我把（1）代进去能求出答案，把（2）代入则x=5与题目要求不符，求讲解。谢谢

@陆旭老师 这道题思路是什么呀？应该怎么做呢？

这道数学题 我想问问数学老师为什么我的两个方法答案都不对 首先 我理解这道题是问事件M或者R只发生一个的概率 我的第一个方法就是用M发生*R不发生+M不发生*R发生 这样哪里出错了 需要怎么改呢？ 我的第二个方法是用总体减去M和R同时发生的概率再减去M和R都不发生的概率，这里哪里出错了 要怎么改呢？ 谢谢老师的回答！

@英吉老师 我想问一下这道题A选项错在了哪里，算是犯了什么错误？

@英吉老师 这一道题里的c选项还是不是很明白哪里错了，请问这句话要是怎么改就算对了呢？

@徐小梅老师，徐老师您好，第4)题，我也看到了“至少2人”这个字眼，也是按照至少2人来算的。但我是这么理解的：原来男女共有12个人，先从5个女生中取2个人，保证了至少有两个女生，所以是C5^2; 接着，再让剩下的3个女生和7个男生合并，共10人，取3个人（此时不论男女都可以），是C10^3。然后合起来就是C5^2*C10^3。

为什么4）不能直接用C5^2 *C10^3?先从5个女生中选2人，再从剩下的10人中选3。这样我算出来的是1200。但是按照图片上老师的方法算的是596。很疑惑，求老师解答一下，谢谢！

为什么分子是5 就一定有一个分母是2的三次方有一个分子是1呢？