Come in, Amy.
Shut the door, please.
This bedroom is very untidy.
What must I do, Mrs. Jones?
Open the window and air the room.
Then put these clothes in the wardrobe.
Then make the bed.
Dust the dressing table.
Then sweep the floor.
- must
must是一个情态助动词，表示"必须"、"应当"，与have to相似，表示不可逃避的义务。在说话人看来，没有选择余地。但是，must带有个人色彩，表示说话人的主观意图。表示个人感情时通常用must。You must…（你必须……）表示说话人说/认为……是必要的。如：
You must sweep the floor.
你必须扫地。（我说这有必要）
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