【题目】—Mr. Johnson, Fm really sorry you waiting for so long a time.
—I know you are very busy at the moment.
A. to have kept B. to keep
C. to be keeping D. to have been kept
在线课程【答案】A
【解析】考查非谓语动词。上句：约翰逊先生，我真的很抱歉让你等了这么长时间。下句：我知道你现在很忙。此处是动词不定式做原因状语，非谓语动词keep的动作明显先于谓语动词，所以用动词不定式的完成式，故选A。