If (it is) necessary, we can give you another chance.
如果必要的话，我们可以再给你一次机会。
(3)名词性从句中的省略
常见的是使用不定式在主动表达中省略动词的施动者，在被动表达中省略助动词、情态动词等。
例：
She will go to Beijing, but I don’t know how (she will go to Beijing).
她将去北京但我不知道她怎么去。
(4)定语从句中的省略
定语从句中也常使用不定式作为省略的手段;当用as引导非限制性定语从句时，常省略系动词。
例1：
All tests require a potential candidate with whom (the tests) to compare DNA.
所有的测试都需要一个潜在的对象，从而可以将DNA与其比较。
例2：
He gave the same answer as (he had given) before.
他给出的答案和以前一样。
三、试题举例
However , it has been found that even people insensitive to a certain smell at first can suddenly become sensitive to it when exposed to it often enough . (05,完型)
They may teach very well , and more than earn their salaries , but most of them make little or no independent reflections on human problems which involve moral judgment . (2006,50)
