关于AB选项，从语义的角度分析。
原划线句的语义是伴随状语修饰主句，表示结果。那么，从语义逻辑上来说，结果与主句就是两句话，说的是两个事情。
但正确答案为B, 定语从句修饰event，从语义逻辑上来说，则这里的修饰部分与event是一件事情，更准确地说，这个事件包含了修饰部分。
因此，根本上的不同是语义的不同。作者的intended 意思是想说“过去某些时候我们祖先经历一件什么样的事件”，而不是说“过去某些时候我们祖先经历了一个事件，导致了什么什么”。是因为破折号后面的部分是用来对前面整句话的解释说明，既然是解释说明，不论解释部分是否简洁，都要解释清楚，不然还是什么解释说明？
而A选项是说“经历了一个事件，导致了什么什么”，重点就在于这句话的重心是“事件”，而“事件”本身是没有解释也没有说明的，“导致了什么什么”不是对“事件”本质的说明，仅仅是事件的结果罢了。因此破折号的后面，也就是解释部分，A选项中最重要的“事件”没有解释，那么这个解释就是失败的。所以A选项本身就不构成对前一句的解释说明。

nevertheless

D和E比错在哪里？是时态的区别吗？

Ron：in general, \"COMMA + prep phrase modifier\" is an adverbial modifier, meaning that it modifies the entirety of the preceding clause.
in this sentence, we don\'t want an adverbial modifier, since it doesn\'t make any sense for this modifier to apply to the entire preceding claus

with 去修饰通常是表伴随，但是题目中很明显是在进一步解释，所以which...要远远优于with...
注意AB选项中it的指代问题 profits 是副词

"after having VERBed" is, in general, a redundant construction -- the word "after" is already there, so "having" doesn't contribute anything.
if you see this construction, you should generally be able to replace it with "after VERBing". it's possible that there are exceptions, but i can't think of any at this time.

eg：The course offered on Wednesdays will fit nicely into your schedule. --> in this example, "offered on wednesdays" is an essential modifier, signifying that there are also other courses.
Offered on Wednesdays, the course will fit nicely into your schedule. --> this time we have a nonessential modifier, indicating that "the course" can stand on its own. this doesn't make sense unless there is only one course.

(d) is incorrect because it purports to modify "the act of congress" with nonessential modifiers (i.e., modifiers that are set off by commas). if that's the case -- i.e., if these modifiers are allowed to be nonessential -- then that means "the act of congress" can stand on its own.
that would imply that there has only been one act of congress, ever.
not good.

注意看时态的parallelism

搞清楚前面的原理之后，题目问你 为什么 小螃蟹 没有挖洞 身上也没有 这些缠绕的藤呢？
直接找原因解释就好， 所以答案文段必须要提到或者映射出小螃蟹的特点。

其实这个政策就是到导致 员工重病才去医生，轻病不让看医生，然后轻病传染同事，过往轻病是可以请假看医生的。所以就是C 。
欢迎批评指正

D是错在for吗？

The issue with choice E is that it's structured the same way, mistakenly suggesting a reference to all such tubes in the first part of the sentence.
Unlike the smog in Mexico City, which is often dense enough to hospitalize or even kill asthmatic children, the air pollution in Houston has never threatened human life.
--> Now it's just "Mexico City smog vs. Houston air pollution".

Unlike smog, which in Mexico City is often dense enough to hospitalize or even kill asthmatic children, humidity is not inherently dangerous.
--> This sentence is a comparison between ALL smog (not just the smog in Mexico City) and humidity.

The real issue with choice E is that it creates a comparison between all tubes (not just the ones in mammals!) and "the tubes in birds".

总是看不出相关因果推理 C排除他因 取非削弱 相关因果推理 结论是一个因果关系
前提：“上过大学等级课程”和“不容易犯罪”之间存在正相关关系
结论：为了减少犯罪率，不应该取消监狱中大学等级的课程
增强结论
A只是单纯的重复 不能增强结论

B比A的finance charges多交3200，加上商品的金额B-A=10,000，因此共计13,200

down payment 首付