工作正常时氟利昂冷剂在压缩机吸气管中吸热流动:()。
A.压力和干度逐渐升高
B.压力和过热度逐渐升高
C.压力降低,干度增加
D.压力降低,过热度增加
参考答案:D
Great changes ()in our country since twenty years ago.
A.have taken place
B.have been taken place
C.took place
D.have been happened
无线电广播采用()方式
A.CDMA
B.SDMA
C.TDMA
D.FDMA