问题补充：
—I must apologize for ahead of time.
—That’s all right.
A. not letting you to know
B. not letting you know
C. letting you know not
D. letting not you know
答案：
A. not letting you to know
(答案→)B. not letting you know
C. letting you know not
D. letting not you know
解析：考察句型。Apologize for (not) doing sth 意为因做（没做）某事而向道歉 for是介词
句意为，--我必须因为没有提前让你知道而道歉。--没关系。
