第21题: [单项选择]The dean of our department is supposed ______ for Florence the day before yesterday. A. to leave B. to have left C. to be leaving D. to have been left 参考答案:B 答案解析:虚拟语气题。be supposed to have done是一种特殊的虚拟语气,相当于should have done,表示过去本应该做某件事而没有做。因此正确答案为[B]。