— I'm sorry to keep you waiting.— Oh,not at all.I here for o

— I'm sorry to keep you waiting.— Oh,not at all.I here for only a few minutes.
— I'm sorry to keep you waiting.
— Oh,not at all.I here for only a few minutes.
[ ]
A.was
B.is
C.have been
D.had been
答案选的是C,但是我没想通,每个选项都要做一下解释.