Supply must have been, can’t, couldn’t have been, have to, had to (be), didn’t have to (be). he knows a lot about flying planes. he must have been a pilot when he was young. vera ………. at the supermarket this morning. i didn’t see her here.

He knows a lot about flying planes. He must have been a pilot when he was young. Vera couldn't have been at the supermarket this morning. I didn’t see her here.