5. must, may (might) 和can表示"推测"的用法

情态

动词 用法 例句 must 只能用于肯定句，表示可能性很大的一种推测，作"肯定""一定"讲 (1)--- Look, someone is coming. Who can it be?

--- It may be the headmaster.

---It can't be him. He has gone to Shanghai.

--- Then it must be Mr Zhang. He looks like the headmaster.

(2)--- What can they be talking about?

--- They may / must be talking about the question raised at the meeting.

(3) --- Can they have finished the work?

--- Yes, they may / must have finished it.

--- No, they can't have finished the work so soon.

--- Then they must have played so much. May /might 用于肯定句中（可能，或许，大概）；用于否定句中（可能不）。表示可能性较小的一种推测 can 表示推测时，只用于否定句和疑问句中