That can't be right.
impossibility
Can you lend me a pen?
request
He can run really fast.
ability
Can I get your bags?
offer
Children can be difficult sometimes.
possibility
You can't watch any more TV.
refusal of request
I couldn't see the road.
past ability
Could I have your autograph?
polite request
The post could sometimes take weeks.
past possibility
Could I get you anything else?
polite offer
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