Choose the right verbs to complete the sentences.

Choose the correct option.

George has been walking without a coat. He [must|may|can't] have caught a cold! I'm sure he'll go down with it soon.

You [must|may|can't] be a straight-A student! I'm sure you aren't good at lots of subjects.

I'm not sure, but I think that Nina [must|may|can't] be the next winner of the competition.

There's no doubt that this bag [must|may|can't] be expensive. The quality is so high!

We aren't convinced! You [must|may|can't] have won that competition, but where's the proof?

It [must|may|can't] be the best day of my life! I'm too stressed out to feel happy.