We must wait here.
We mustn't wait here.
You may sit here.
You may not sit here.
They can go by plane.
They can't go by plane.
We can meet you later.
We can't meet you later.
She should sit near the window.
She shouldn't sit near the window.
She can play the piano well.
She can't play the piano well.
He may leave on Wednesday.
He may not leave on Wednesday.
I can understand him easily.
I can't understand him easily.
We should tell her about it.
We shouldn't tell her about it.
We must do the same thing again.
We mustn't do the same thing again.