— should we clean the library? —Twice a week.A. How manyB. How muchC. How longD. How ofte

问题补充：

— should we clean the library?

—Twice a week.

A. How many

B. How much

C. How long

D. How often

答案：

A. How many

B. How much

C. How long

(答案→)D. How often

解析：本题回答语表示的是频率，对此提问用how often，故本题选D。