【问】 The only thing to do was ask them to come half an hour later than the other guests. (NewConcept English，Book 3，L. 60)
 唯一措施乃是邀请他们的时间比其他客人迟半小时。
 据我所知，充当表语的动词不定式是要带动词不定式符号to的。但是，上句中的充当表语的动词不定式ask…却没有带to。如何解释这种现象。
 【答】 充当表语的动词不定式省略不定式符号to是有条件的：在主语部分中必须含有动词do。例如：
 1. What I want you to do is(to) help Mary with her homework.
 我要你做的事就是帮助玛丽做作业。
 2. What you should have done was (to) submit the problem to the committee for discus-sion.
 你本应当做的事就是把问题提交委员会讨论。
 3. The only thing you have to do is(to)press the button.
 你要做的唯一的事情就是按一下按钮。
 4. The best thing you can do now is write her an apology.
 你现在所能做的最恰当的事情，就是向她写一份道歉书。
 5. All I want to do was(to) help him. (CGEL)
 我所想要做的就是帮助他。
 6. Anything we could do was empty the bottle. (Reader's Digest)
 我们能做的事情只是把瓶子倒干净。
 7. All you have to do is get rid of the junk.
 你必须做的事情就是清除这些破烂东西。
 8. What I did was learn the language. (GCE)
 我所做过的事情，就是学习语言。
 9. All you have to do is wait for the right opportunity...(BBC Modern English)
 你需要做的事情，就是等待恰当的机会。
 我们发现，当all做主语时，如定语从句含有say，充当表语的动词不定式有时也可省略动词不定式符号to：
 All they said is hurry up.
 他们所说的话就是赶快。
 在下列句子里就不能省略to：
 1. All I wanted was to help him. (CGEL)
 我所想的事情就是帮助他。
 2. The only way that they can preserve their history is to recount it as sagas——legendshanded down from one generation of story-tellers to another. (New Concept English，Book 4，L.1)
 他们保存自己历史的唯一方法就是采用讲故事的办法：由讲故事者把类似英雄故事的民间传说一代代传下去。