问题补充：
—If you have any trouble, be sure to call me.— _.
A. I am glad to hear that
B. I will. Thank you very much
C. I have no trouble
D. I will think it over
答案：
A. I am glad to hear that
(答案→)B. I will. Thank you very much
C. I have no trouble
D. I will think it over
解析：根据本句If you have any trouble, be sure to call me.可知if 引导的条件状语从句，在if 引导的时间状语从句，主句为祈使句，而从句用一般现在时，代替一般将来时，故选答案为B
