Unless to speak, you should remain silent at the conference.
A. invited
B. inviting
C. being invited
D. having invited
网友回答
(答案→)A. invited
B. inviting
C. being invited
D. having invited
解析：原句意思是，除非你被邀请发言，否则你应该在会议上保持安静。连词后可以直接加现在或过去分词，由主动被动决定．由于＂你＂是被邀请的，所以应该用过去分词，故选A。