Complete the student's shocked text message to their friend with the correct modal verb.

That guy in the mosh pit ___ be Professor Higgins! He is supposed to be giving a lecture in Tokyo right now!

The correct answer is can't.

When we are almost certain that something is impossible or not true, we use can't (or cannot).

Careful! A very common mistake is to use "mustn't" as the opposite of "must" for deduction. However, "mustn't" is only used for prohibition (e.g., "You mustn't walk on the grass"), never for deduction!