问题
选择题
This problem is said _______ three times, but he still can’t understand it.
A．to have been explaining
B．to have explained
C．having been explained
D．to have been explained
答案
D
题目分析：句意：这个问题被解释了三次了，但是他还是不明白。这里是sth be said to do，故排除C；这里This problem与explain之间是被动关系，故排除AB；根据句意故选D。