稳定的水位流量关系是应满足同一水位的流量等于面积与流速乘积，误差应在（）以内。
A.±3%
B.±5%
C.±10%
D.±15%
参考答案：A
—Maria, what're you going to be when you grow up?
—A _______.I like to help doctors and take care of the sick. [ ]
A. nurse
B. reporter
C. teacher
D. policewoman
要改变物体运动状态，就必须对它加______ 。若在水平地面上放一个重20牛顿的物体，用2牛顿的水平拉力使物体在水平面上作匀速直线运动，该物体受到的摩擦力是______ 。
