题目

要调查某校九年级550名学生周日的睡眠时间，下列调查对象选取最合适的是（     ）   A．选取该校一个班级的学生              B．选取该校50名男生   C．选取该校50名女生                   D．随机选取该校50名九年级学生 答案：D解析:随机抽取有代表性。 My sister met him at the Grand Theater yesterday afternoon, so he ________ your lecture.    A. couldn’t have attended                B. needn’t have attended    C. mustn’t have attended                 D. shouldn’t have attended