By the time he was 38 he had become principal of university.A. /; anB. /; aC. a; anD.

问题补充：

By the time he was 38, he had become principal of university.

A. /; an

B. /; a

C. a; an

D. a; the

答案：

A. /; an

(答案→)B. /; a

C. a; an

D. a; the

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