透平膨胀机制冷的适宜温度为小于()℃,否则机械制冷的效率可以与之竞争。
A.-20
B.-40
C.-60
D.-80
参考答案:D
Wu Rui likes keeping clean very much. She _______ a bath twice a week.[ ]
A. takes
B .take
C. have
D. washes
在土中挖坑埋渗压计,宜采用砂包裹体法,即在坑中用细砂将渗压计包裹,并用水饱和后再填土。