问题：
—Do you know when Mr. Green will come?
—Sorry, I have no idea. But if he _____, I will call you.
[ ]
A. comes
B. is coming
C. will come
D. come
—Do you know when Mr. Green will come?
—Sorry, I have no idea. But if he _____, I will call you.
B. is coming
C. will come
D. come
—Sorry, I have no idea. But if he _____, I will call you.
[ ]
A. comes B. is coming
C. will come
D. come
参考答案：