Question

---May I go out to play with my friends now, Dad?
---No. You ______ let your mother know first.
A. may                     B. need                    C. must

Answer 1

C

解析试题分析：句意：我可以和朋友一起出去玩吧，爸爸？不，你必须首先让你妈妈知道。May可以；need需要；must必须。所以选C。
考点：考查情态动词。