问题补充：
This problem is said three times.
A. to have been talked
B. to have discussed
C. having been discussed
D. to have been talked about
答案：
A. to have been talked
B. to have discussed
C. having been discussed
(答案→)D. to have been talked about
解析：此处使用的是不定式的完成被动式。表示“曾经被讨论过三次”。
