Can, Could, Be able to

Can

Is used to talk about possibility. e.g. ‘Can you meet me at 5?’
Is used to talk about ability. e.g. ‘I can ride a bike’. 
Is used to make informal requests and orders. e.g. ‘Can you bring me my jumper?’
Negative forms: can’t and cannot.

Could

talks about past abilities. e.g. ‘When I was a child I could do handstands’.
makes formal requests. e.g. ‘Could you fax me that document by Tuesday?’ 
Negative form: couldn’t.

Be able to

Is sometimes used instead of can or could when we talk about a particular situation.
Can be used with all tenses. e.g. ‘I will be able to see you next week’. 
Negative: isn't /aren't/ wasn't/weren't / won't be able to etc 

EXERCISES: EX1, EX2, EX3, EX4, EX5