This is empty bottle. But it is useful one.A. a; aB. an; aC. an; theD. a; an

This is empty bottle. But it is useful one.
A. a; a
B. an; a
C. an; the
D. a; an

A. a; a(答案→)B. an; aC. an; theD. a; an解析：句意：这是一个空瓶子。但是他是一个有用的瓶子。结合语境可知前文泛指任何一个空瓶子，故用不定冠词，empty词首音素是元音，故不定冠词用an。下文泛指任何一个有用的瓶子，也用不定冠词。Useful词首音素是辅音，故不定冠词用a。选B。

感谢回答，我学习了