We were told not to touch the equipment in the laboratory unless ________.A.allowed to doB.allowing to doC.allowed toD.allowing to
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C解析考察状语从句的省略。Unless后面省略了we were.不定式符号to后面省略了touch the equipment.当状语从句的主语和主句主语一致的时候，可以把主语和系动词be一起省略.完整的形式应该是：unless we were allowed to touch the equipment.句意：我们在告知在实验室里不要碰任何东西，除非我们被允许。