You can’t be serious.
She can’t be a traitor.
He can’t have made such an important discovery.
The teacher can’t have forgotten to correct our homework.
The work can’t be too difficult for my friend.
Jane can’t have made such a mistake.
The cat can’t have eaten all the fish.
Our papers can’t have been so poor.
You can’t have believed such a silly lie.
He can’t have stolen the money.
They can’t have heard the story before.
She can’t be good at physics.