[单项选择]

Once a man and his wife worked for an old man. There was a big box in the old man’s living room. The old man pointed to the box and said, "There’s only one thing you (1) do. Don’t open the box. " (2) saying this, he left his home.The woman said to her husband," There must be (3) expensive in the box. Let’s open it, shall we" Her husband said (4) to her. But the woman didn’t give up her (5) . One day, she decided to find out (6) was in it. Her husband didn’t stop her. She opened the box and looked inside. To her surprise, she found nothing in the box. She tried hard to close it, but she (7) That evening the old man came home and found the box was (8) . He was very (9) and asked the woman and her husband to leave his home."But there was nothing in the box," the woman said. "We haven’t taken anything at all. "The old man (10) them, "The box is not important, but I cannot believe you. That’s
A. may not
B. mustn’t
C. dare not
D. needn’t