这个要总结起来未免太多了。我先比较一下like和as做比较的用法。
这些点是我根据曼哈顿语法和CD上一些大神的点总结而成，转载请打招呼。
一) Like
1. like 可以修饰名词和动词(I danced LIKE you last night.)，但 like 后只能跟名词或代词。2. Like 的位置对句义有影响，使用 like 的时候要注意是否会造成歧义:
歧义:I want to coach drivers LIKE Greg Louganis.
=I want to coach drives WHO ARE like Greg Louganis.
或= I want to coach drivers IN THE SAME WAY AS Greg Louganis coaches drivers.
不会造成歧义: I want to coach drivers, LIKE Greg Louganis. (注意 like 前的逗号，这种情况下比较的是主语)= Like Greg Louganis, I want to coach drivers. (他 coaches drivers，I want to do so.)这个是GMAT考试中经常遇到的情况
3. Unlike 的使用也很常见:
Right:Unlike you, I danced last night. (You did not dance last night.)
在不引起歧义的情况下，unlike 也可以向 like 一样放在句尾。放句尾时，常常把 unlike 后跟的名词与主语想比较:
Right: Most materials under a wide range of conditions resist the flow of electric current to some degree,UNLIKE superconductors which demonstrate zero electrical resistance.
(二)AS
as 可以作为连词和介词
1. as 作为连词，有三种用法
(1) Duration as: AS I strolled to the store, I smelled the air. (while, during) 当...时候(2) Causation as: I will not tell you, AS you already know. (since, because) 因为
(3) Comparison as: You should walk AS she wants you to. (in the same way) 正如
表比较的 as，是连词 as 在 GMAT 最重要的用法，通常和 “just, so” 、甚至 “so too” 一起使用，连接 2个句子，极少数情况下 as 后可跟一个短语:
Right: JUST AS the trains were late yesterday, the buses are late today.
Right: JUST AS the trains were late yesterday, SO TOO are they late today.
as 后加短语:
Right: AS in the previous case, the judge took an early break.
2. AS 作为介词，表“作为，当” 而不是“象”，因词介词 as 不是在做比较。介词 as 后面加名词或名词短语，有三种用法
(1) Function as: As your leader, I am in charge. (=in the role of)
(2) Equation as: I think you AS my friend. (= you are my friend)
(3) Stage as: AS a child, I thought I could fly. (= when I was)
3. as 表比较时，as 后得跟一个从句。要变成从句，加一个动词即可
As 表 similar to: I will jump up AS a clown. (= in a clown suit!)Page 22 of 54
As 比较比较: (1) I will jump up AS a clown MIGHT. (=like a hypothetical clown)(2) I will jump up AS clowns DO. (= like actual clowns)
4. 举例只能用 As(或 such as)，不能用 like
Wrong: I enjoy fast food LIKE hamburgers. (=fast food SIMILAR TO hamburgers)Right: I enjoy fast food SUCH AS hamburgers.
好了，今天就写到这个，不过还是要劝大家，在考试前一定要多刷一下历年考试真题资料，这样会对考试很有帮助，祝大家都能取得一个不错的成绩。
