His father teaches English at middle school but I don’t know which one.A. aB. an C. theD.

问题补充：

His father teaches English at middle school but I don’t know which one.

A. a

B. an

C. the

D. /

答案：

(答案→)A. a

B. an

C. the

D. /

解析：句意：他的父亲在一所中学教书，但我不知道是哪一所。泛指一所学校，用不定冠词a。所以选A。