产程中最主要的产力是()
A.肛提肌收缩力
B.膈肌收缩力
C.子宫收缩力
D.腹肌收缩力
E.会阴肌收缩力
参考答案:C
Yang Liwei ______ about 21 hours travelling around the earth 14 times in the spaceship.[ ]
A. took
B. spent
C. paid
D. cost