Ответ:
1) а (must)
2) c (needn't)
3) d (could you)
4) а (may)
Объяснение:
1) Soldiers must obey their commander's orders.
2) I'll come at 7 tomorrow. - No, you needn't come that early, we start much later.
3) How could you be so rude with your teacher?
4) May I ask you how old you are?