请教英语单选题I can't understand -- a decision until it is too late

The answer is C.Ask yourself,what can't I understand,"him" or "his postponing?" You don't understand his decision to postpone,not that you don't understand him.Thus,it should be "his postponing."
D is also not the answer,unless a comma is inserted between postponing and making,like so,"I can't understand his postponing,making a decision until it is too late."
So C is the only grammatically correct answer to the above sentence.