There is a(n) ________ of peace and calm in the country, quite different from that of a big city.[ ]

A. conditions

B. situation

C. atmosphere

D. moment

为了获得-140℃的蒸发温度，（）为适宜的复迭式循环组合方式。

A.R22单级+R13单级

B.R290单级或两级+R13单级

C.R22两级+R13单级或两级

D.R22两级+R13单级+R14单级