There is backpack on the desk. It belongs to Tom.A. a B. an C. the D. /

问题补充：

There is backpack on the desk. It belongs to Tom.

A. a

B. an

C. the

D. /

答案：

(答案→)A. a

B. an

C. the

D. /

解析： 根据题意可知此处泛指任何一个背包，且backpack词首音素为元音，故选A。