一,be 的用处很多,例如:
1. 作系词.I am a student.
2. 作助动词,构成现在进行时.I am working.
3. 作助动词,构成被动语态.I was surprised by his words.
4. 与 to 共同组成情态动词,表示“应该”.You are to come earlier.
5. 与 about to 组成情态动词,表示“即将”.He is about to leave.
二,to 可以用作介词,有具体词义.也可以用来构成动词不定式,无词义.
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