— do you go to the library?—Twice a week. A. How muchB. How manyC. How oldD. How often

问题补充：

— do you go to the library?

—Twice a week.

A. How much

B. How many

C. How old

D. How often

答案：

A. How much

B. How many

C. How old

(答案→)D. How often

解析：How much多少钱;How many多少个;How old多大;How often多久一次. 根据下文, 一周两次. 可知上文提问的是频率, 故选D.