问题补充：
David apologized for to inform me of the change in the plan.
A. his being not able
B. him not to be able
C. his not being able
D. him to he not able
答案：
A. his being not able
B. him not to be able
(答案→)C. his not being able
D. him to he not able
解析：介词for后应用动词的-ing形式，排除B、D；所有非谓语动词的否定词not都应加在非谓语动词之前，即not to do ,not doing, not having done, not done,故选C。
