Fill in the correct modal verb
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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?