将压缩空气的压力转变为制动动力的部件是（）。
A.空气压缩机
B.总风缸
C.副风机
D.制动缸
参考答案：D
—Recently I have read many _______ about the droughts in the south of China.
—Oh, the farmers will have a bad harvest this year. [ ]
A. reports
B. news
C. novels
D. speeches
自然循环锅炉中，汽水主要靠水和蒸汽的密度差产生的压头而循环流动
