must/ m^st /

1.aux vb
(expressing importance or necessity) 必须

The doctor must allow the patient to decide.
医生必须让病人来决定。
2.aux vb
(expressing intention) 得

I really must be getting back.
我真得回去了。
3.aux vb
(expressing forceful suggestion) 一定要

You must see my new guitar.
你一定要看看我的新吉他。
4.aux vb
(expressing anger in question) 偏要

Must you be so careless?
你偏要这么粗心吗?
5.aux vb
(expressing presumption) 一定

Russell must be one of the youngest ever Wembley referees.
拉塞尔一定是温布利体育场上历来最年轻的裁判之一。
He must have forgotten to pick up the tickets.
他一定忘记去取票了。
6.aux vb
(expressing sympathy) 一定

Sit down, you must be exhausted.
坐吧,你一定累坏了。
7.aux vb
you must be joking (expressing surprise or shock) 你准是在开玩笑

I must be mad!
我准是疯了!
8.noun [inf] 
to be a must (necessity) 是必备之物

Rubber gloves are a must if your skin is sensitive.
橡胶手套对于敏感皮肤是必备之物。
if you must
如果你坚持要
if you must know
如果你一定要知道的话