—Where did you get The Frog written by Mo Yan?—I picked it up from a bookshop online if yo

问题补充：

—Where did you get The Frog written by Mo Yan?

—I picked it up from a bookshop online if you know.

A. must

B. will

C. can

D. shall

答案：

(答案→)A. must

B. will

C. can

D. shall

解析：A 考察情态动词，句义：如果你非要知道，我是在网店里买到的这本书。Must表示非得，偏要。