I'm sorry to have kept you______________.

[    ]

A. wait   B. waited   C. waiting   D. to wait

I’m sorry to have kept you _____ so long. Now let’s get down to business.

A. waiting　　 B. to wait　　　 C. have waited　　　　　 D. from waiting

I'm sorry to have kept you ________ for so long a time.

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I'm sorry ____ so long, I forgot to tell you in advance where I had put my key.

　　A. to keep you wait           B. to keep you waiting

　　C. to keep you waited         D. to have kept you waiting