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：考查非谓语动词作状语。You和invite构成被动关系，所以使用过去分词。句意：如果你没有被邀请发言，在会议上你应该保持沉默。