问题补充：
--- Must we find out the reason today?
--- No, you .
A. mustn’t
B. don’t have
C. don’t have to
D. needn’t to
答案：
A. mustn’t
B. don’t have
(答案→)C. don’t have to
D. needn’t to
解析：句意：---我们今天必须找出原因吗？---不，你不必了。must表示必须，否定回答时用needn 或don have to.（不必). mustn 表示不许可。例如：You must get to the station before 3, otherwise you will miss the train. Must I hand in my homework tomorrow? No, you needn . You can turn it in the day after tomorrow. You mustn smoke in the hospital.由句意可知选C。
考点: 考查情态动词的用法。
