There is useful book on the desk.A. aB. anC. theD. /

问题补充：

There is useful book on the desk.

A. a

B. an

C. the

D. /

答案：

(答案→)A. a

B. an

C. the

D. /

解析：考查冠词。句意：桌子上有本书很有用。useful的发音开头/ju:/是辅音所以冠词用a，答案选A。