I couldn't swim when I was younger.
I wasn't able to swim when I was younger.
He can run very fast.
He is able to run very fast.
We couldn't cook pizza.
We weren't able to cook pizza.
We can speak German fluenty.
We are able to speak German fluently.
He can go to your party today.
He is able to go to your party today.
They can speak English perfectly.
They are able to speak English perfectly.
She couldn't sleep last night.
She wasn't able to sleep last night.
He can't perfom in school plays.
He isn't able to perform in school plays.
She couldn't visit her grandma because she was too busy.
She wasn't able to visit her grandma because she was too busy.
We can't go out today because it is going to rain.
We aren't able to go out today because it is going to rain.
I couldn't go to school because I was sick.
I wasn't able to go to school because I was sick.