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Unless ____ to speak,  you should remain silent at the conference.

A invited         B inviting           C being invited    D having invited

Unless ________ to speak, you should remain silent at the conference

 A. invited         B. inviting      C. being invited    D. having invited

6.____,the experiment will be successful.

Unless _____ to speak, you should remain silent at the conference.

  A. invited                        B. inviting                            C. being invited               D. having invited