A:was he able to make himself hear
B:he was able to make himself hear.
C:he was able to make himself heard
D:was he able to make himself heard .
“风吹草低见牛羊”.下列有关草和羊的描述.正确的是( )
一物体沿水平面做匀速直线运动,物体受到的摩擦力是20N,则物体受到的拉力是____ N;如果拉力增大到25N,物体受到的摩擦力为____N.