She couldn't sleep last night.
She wasn't able to sleep last night.
She couldn't visit her grandma because she was too busy.
She wasn't able to visit her grandma because she was too busy.
He can run very fast.
He is able to run very fast.
He can go to your party today.
He is able to go to your party today.
I couldn't swim when I was younger.
I wasn't able to swim when I was younger.
I couldn't go to school because I was sick.
I wasn't able to go to school because I was sick.
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't perfom in school plays.
He isn't able to perform in school plays.
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.
They can speak English perfectly.
They are able to speak English perfectly.