In our class the student leaders are on duty every few days.A. the; a B. a; theC. a; aD

问题补充：

In our class, the student leaders are on duty every few days.

A. the; a

B. a; the

C. a; a

D. 不填; 不填

答案：

A. the; a

B. a; the

C. a; a

(答案→)D. 不填; 不填

解析：考查冠词固定词组。On duty值日；every few days每几天；句意：在我们班级里，班长每几天就值日一次。故D正确。