Question

18. You will have to go over the books again. You
might have been concentrating/ can't have been
concentrating when you looked at them the first time.
19. I just called the office but I guess they may
have may be having a lunch break.
20. If you carry those heavy suitcases you must
might injure yourself. fill with models​

Answer 1

Answer:

19. i just called them to lunch break but i guess they may be having office work

20. if you carry those heavy suitcases you might injure yourself

Explanation:

they may / have may =have may => 19

must/might = might  =>20