羊水栓塞的高发因素是：
A．高龄产妇
B．多产妇
C．过强宫缩
D．急产
E．初产妇
参考答案：A,B,C,D
—What's the matter with John? He has been sitting there for hours．
—A postcard from his father an attack of home - sickness in him．
A．took up
B．set off
C．brought in
D．built up
什么叫节流？常用的节流装置有哪些？
