The English meaning of 1 cannot2 must not3 should not
As such is the case, I am sorry I can't accept your kind invitation.
Sorry, but can you show me the way to the next village?
I can't bring myself to do such a thing.
I'm very sorry, we can't accept your request.
I felt so sleepy that I could hardly keep my eyes open.
You can't drink seawater because it is too salty.
The problem is we can't use our car on that car.