髋关节中心性脱位宜采用持续牵引治疗,时间一般是()。
A.3~4周
B.4~6周
C.6~8周
D.8~10周
E.3个月以上
参考答案:C
It _________ that I met an old friend of mine on my way home.[ ]
A. took place
B. happens
C. happened
D. was happened
机组启动初期,主蒸汽压力主要用()来控制。
A、调节汽轮机旁路系统
B、调节锅炉燃烧
C、锅炉和汽轮机共同调节