第31题: [单项选择]The Gadfly was too much exhausted to wake easily ______. A. when once asleep B. as once asleep C. while once sleeping D. when once sleeping 参考答案:A 答案解析:[解析] 状语从句中的谓语动词是be,而主语又与主句中的主语相同时,或者从句的主语是it,可以省略从句中的动词be和主语,否则,不可省略。本句从句的主语和主句主语相同,而且谓语动词是be, aslee