This is key and that is eraser.A. a aB. a anC. an aD. the an

问题补充：

This is key and that is eraser.

A. a, a

B. a, an

C. an, a

D. the, an

答案：

A. a, a

(答案→)B. a, an

C. an, a

D. the, an

解析：此题考查不定冠词的基本用法。）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。