I have useful knife and my sister has eraser.A. a; anB. an; aC. a; aD. an; an

问题补充：

I have useful knife and my sister has eraser.

A. a; an

B. an; a

C. a; a

D. an; an

答案：

(答案→)A. a; an

B. an; a

C. a; a

D. an; an

解析：useful词首音素是辅音，故不定冠词用a；eraser词首音素是元音，故不定冠词用an，选A。