可逆式换热器冷段增设环流流道的主要目的是()。
A.调节膨胀空气量
B.增加可逆式换热器冷端冷源
C.缩小冷端温差,保证可逆式换热器自清除
D.调节膨胀机机前进气温度
参考答案:C
He had a lot of friends, but none of _____ could lend him any money.
A.whom
B.them
C.which
D.who
基本缝合法有三类,分别是?