could是过去式

where 只能修饰实体的地点，如area, site, country, society；
对于metaphorical place时，如condition, situation, case, circumstances, arrangement用 in which，不用where；
修饰在某物，如I have a book/company in which……等，用in which，不用where

in societies where little salt is consumed,如果改成in which，则是in societies in which，很奇怪，用where更优

A is among the most famous works, 英语常用句型，表示某物是最著名的作品之一。

考察as ... as ...的平行结构。E：此题的原意是became well known for ... and for ...，而为了和 as ... as ... 搭配使用，需将结构变化为 became as well known for ... and for ... 。而如果保持结构不变，则是became well known as for ... as for ... ，但此结构明显不如 became as well known for ... and for ... 好，但两者都是正确的。

refrain不认识影响答题
refrain 克制
refrain from 克制不去做某事

可不可以这样做呢：令x-y-(x+y)=x-y-x-y=-2y,由条件（2）y＜0，那-2y＞0，所以x-y＞x+y,分子大于分母，不就式子大于1了吗？为啥条件2不对呢？

promise是个影响力大的词语，承诺了的很可能会发生，接to do。
the promise to do sth, 做某事的诺言；
the promise of sth，如：government's promise of lower taxes

BC还有个问题在于只讲了陆蛇和海蛇，但其实文章还大篇幅讲了树蛇，所以BC都是文章细节，不是主旨

B，which 跳跃 the number rises and falls修饰主语the number，跳得太远了。

in 1970 is different from in (early/late)1970's
1970年，1970年代

题目问的是当下列哪项发生时，gap将被缩小，就是字面上缩小的意思，不用考虑是怎么引起的缩小

by doing sth，by sth，by不接的名词，如：by improving而不说by the improvement
through表示穿过立体的物体；表示通过……方式，through可以接动名词，through the improvement，不接doing

A，“生物性质增强繁殖率和存活率”是恒久的事情，类似于真理，看不到终点，所以不用名词，用从句。
他们被偏爱因为他们增强了繁殖率和存活率，ok

where they thus automatically inform the operator=the calls thus automatically inform the operator in the line，在电话线里通知打电话的人，错误

???

small quantities of spices的核心词是spices，small quantities 做数量定语修饰spices

prepare sb for sth
preparation for sth
enhance the preparation的表达不好

不知道a line of reasoning啥意思 但是不影响做题，前边四个选项都排除了。。。

定语从句啊，傻了。。。。脑子不转了。。。

little of类似于a little of，接不可数名词
a few of/few of接可数名词复数