题目

--There is somebody at the door．Who _________ it be? Is it the postman? --No，it _________ be him．It's just seven o'clock． It's too early． A．might；can't          B．will；won't           C．may；mustn't         D．must；mar not 答案：A与动物细胞相比较，植物细胞特有的结构是（ ）A．细胞膜 B．细胞质 C．叶绿体 D．细胞核