None of the attempts to specify the causes of crime explains why most of the people exposed to the alleged causes do not commit crimes and, conversely, why so many of those not so exposed have.
这个问题很简单,在前后两个分句做比较的时候一般后面那个被简化的分句的助动词应该根据前一个分句的助动词来给出。 比如: A did as B did A can as B can A is as B is 但是如果后面这个简化的分句给出了特定的时间状语,就必须考虑把后面这个时间状语考虑进去。 比如: A is *** as B was ten years ago A can do *** as B could ten years ago 拿这个原则去套GMAT的所有题目,无一漏网!
首先,必须搞清楚常考的一些助动词:be, have, shall (should), will (would), do, should have, would have 等。
其中特别需注意的: be 既是系动词,又是助动词,那么什么时候是助动词呢,主要是与实意动词一起构成各种时态和被动语态:be doing/have been doing/had been doing 一般时和完成时的进行时态;be done被动语态(注意有各种时态和语态) 还有do本身也可以是实意动词。