—Can I go to the park Mum?—Certainly. But you be back by six o’clock. A. can B. may C. m

问题补充：

—Can I go to the park, Mum?

—Certainly. But you be back by six o’clock.

A. can

B. may

C. might

D. must

答案：

A. can

B. may

C. might

(答案→)D. must

解析：考查情态动词的用法。同意孩子去公园，但是有要求：必须在6点之前回来。must“一定，必须”。