---do the students exercise a week ?---Once or twice.A. How oftenB. How longC. HowD. How m

问题补充：

---do the students exercise a week ?

---Once or twice.

A. How often

B. How long

C. How

D. How many times

答案：

A. How often

B. How long

C. How

(答案→)D. How many times

解析： A.多久一次 B.多长 C.怎样 D.多少次。根据答语：一次或者两次。可知选D。