A. Can is used to say that someone has the ability to do something .
The negative is can’t ( cannot ) : You can see the ocean from our bedroom window .
Can you speak any foreign languages?
I’m afraid I can’t come to your party next Friday?
=>BE ABLE TO is possible instead of can, but can is more usual :
Are you able to speak any foreign languages?
but can has only to forms. Can ( present ) and could ( past ).
=>>So sometimes you have to use “BE ABLE TO” :
I haven’t been able to sleep recently.
Sue might not be able to come tomorrow.
I’m very busy today, but I should be able to meet with
=>COULD is used to say past ability :
My grand father could speak five languages. When Joe was 16 years old. He could run 100 meters in 11 seconds.
but if you mean that someone managed to to do something
in one particular situation, you have to use WAS / WERE
=>ABLE TO :
The fire spread through the building very quickly, but everyone was able to escape. They didn’t want to come with us at first, but finally we were able to persuade them.
=>COMPARE COULD and WAS ABLE TO :
Jack was an excellent tennis player. He could beat anybody. But once he had difficul game against Bob. Bob played very well, but in the end Jack was able to beat him.
=>>NOTE :THE Negative COULDN’T is possible in all situation.
My grandfather couldn’t swim.
We tried hard but we couln’t persuate them to come with us.