could/kud/

1.aux vb

we couldn't go to the party (referring to past) 我们没能去参加聚会

last year we couldn't afford a holiday
去年我们度不起假
he could be very unkind
他可能会很刻薄
he couldn't read or write
他不会读也不会写
we could hear him whistling
我们能听到他正在吹口哨
she said she couldn't hear me
她说听不见我说的话
2.aux vb

he could be in the library (possibility) 他可能在图书馆

I couldn't be happier
我再高兴不过了
he could be released next year
他明年可能被释放
you could have been killed!
可能你连命都没了!
the accident could have been caused by an oil leak
事故可能是由石油泄漏引起的
3.aux vb

if we had more time,I could finish this (in conditionals with "if") 如果有更多时间,我能够完成的

we'd have a holiday, if we could afford it
如果能支付得起的话,我们就去度假了
4.aux vb

(in offers,suggestions,requests) 可以

I could call a doctor
我可以叫个医生
we could always go to the cinema
我们还是可以去看电影
couldn't you give him a call?
你可不可以给他打个电话?
could I borrow the car?
我可以借一下车吗?
if I could just interrupt you for a minute
我是否可以打扰你一小会儿
he asked if he could make a phone call
他问是否可以打个电话
5.aux vb

you could at least be polite! (emphatic) 你至少可以礼貌点儿!

you could have told me!
你早该告诉我!
I could scream!
我真 想大叫!
how could you have lied to me?
你怎么能向我撒谎呢?