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

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

A．invited         B．invite        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

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

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

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