A：took, would feel
B：had taken, felt
C：had taken, would feel
D：took, would have felt
上浮的物体和下沉的物体在水中都受到____的作用，我们可以感受到浮力的存在，可以用____测出浮力的大小。
为粉碎“四人帮”奠定了群众基础的事件是( )
