A:细绳剪断瞬间,a所受摩擦力也立刻发生变化
B:细绳剪断瞬间,b所受摩擦力不可能为零
C:a所受的摩擦力一定不为零
D:b所受的摩擦力一定不为零
open的意思是 ____.
When I entered the room, I found he was b____ in his work, so he didn't notice me come in.
如图所示,当歼﹣15舰载机起飞离开“辽宁舰”后,“辽宁舰”所受到的浮力将____ ,以舰载机为参照物“辽宁舰”是____的.