分娩时的主要产力是 （）
A.腹肌收缩力
B.腹肌和膈肌收缩力
C.肛提肌收缩力
D.子宫收缩力
E.骨骼肌收缩力
参考答案：D
The teacher asked me .
A．where do I come from
B．that my favourite subject is English
C．what did I like best
D．if I could speak Italian
统一式燃烧室
