There is Mr. Smith at the door who wants to speak to you.A. a someB. certainC. some aD. a

问题补充：

There is Mr. Smith at the door who wants to speak to you.

A. a some

B. certain

C. some a

D. a certain

答案：

A. a some

B. certain

C. some a

(答案→)D. a certain

解析：句意：在门口有位想要跟你说话的史密斯先生。certain某，某一； a certain Smith 一个叫做史密斯的人。some〔用于单数普通名词前〕(有)一个(人、物、时间)。 He went to some place in Africa. 他到非洲一个地方去了。We must find some way out of it. 得想一个方法逃脱才行。some 是指完全不知道的事物而言， a certain 则是在知道而故意不说时、或轻蔑地说‘某一个…’时用,故选D。

考点: 考查不定代词的用法。