产后出血的主要原因是()。
A.子宫收缩乏力
B.软产道裂伤
C.胎盘因素
D.凝血功能障碍
E.药物使用不当
参考答案:A
I had _________ entered the classroom when I noticed the headmaster was sitting at the back.
A.still
B.yet
C.sooner
D.hardly
转K6型转向架下旁承整垫板总厚度为()。
A.2~25mm
B.3~25mm
C.4~25mm
D.5~25mm