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
网友回答
A. to have been explaining
B. to have explained
C. having been explained
(答案→)D. to have been explained
解析：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。