下列部件中（）可以使空调系统内产生低压并同时使低压的制冷剂提高压力和温度。
A.压缩机
B.恒温膨胀阀
C.蒸发器
D.冷凝器
参考答案：A
—There's somebody at the door. Who _____ it be? Is it a postman?
—No, It _____ be him. It's just seven o'clock. It's too early. [ ]
A. may; can't
B. will; won't
C. may; must
D. must; may not
毕节地区水能资源丰富，理论蕴藏量达221.21万千瓦，己开发156万千瓦，把己开发水能资源用四舍五入法保留两个有效数学并且用科学记数法表示应记为（ ）千瓦．
A．16×105
B．1.6×106
C．160×106
D．0.16×107
