当铜排链过载，送料阻力超过保险销所能承受的（）时，保险销就会被剪断。
参考答案：剪切力
______ herself in looking after the newly-born twins, she had to sacrifice her career to stay with her kids.
A．Occupied
B．Being occupied
C．Having been occupied
D．Occupying
人们往往用物流成本占GDP 的比重来衡量一个国家物流管理水平的高低，这种物流成本指的就是社会物流成本。( )
