第8题: [单项选择]He once told me that no acrobat could ever perform those daring feats unless ______ very young. A. to be trained B. being trained C. trained D. be trained 参考答案:C 答案解析:题意为他曾经告诉我这种惊险动作一般杂技演员是不可能表演的,除非从小受过训练。在条件状语从句中,如果从句主语与主句中的主语一致,或主语是代词it,那么从句中的be及其主语常常可以省略。