old man behind Mary is university teacher.A. An anB. A theC. The aD. The an

问题补充：

old man behind Mary is university teacher.

A. An, an

B. A, the

C. The, a

D. The, an

答案：

A. An, an

B. A, the

(答案→)C. The, a

D. The, an

解析：此题重点考查冠词的基本用法。不定冠词有a和an两种：a用于辅音音素开头的词前，an用于元音音素开头的词前。定冠词the表示特指。