多项式y²+4加上一个单项式后，使它能成为一个二项整式的完全平方，则满足条件的单项式有（    ）

下列关于实验现象的描述，准确的是（  ）

如图所示，abc是光滑的轨道，其中ab是水平的，bc为与ab相切的位于竖直平面内的半圆轨道，其半径R=0.30m．质量m₁= $\frac{\sqrt{14}}{10}$ kg的小球A静止在轨道上，另一质量m₂=0.60kg的小球B以水平速度v₀=2 $\sqrt{14}$ m/s与小球A正碰．已知相碰后小球A经过半圆的最高点c落至轨道上距b点为l=4 $\sqrt{2}$ R处，重力加速度g取10m/s²，求：

    I have a friend. His name is Jack. ③He is healthy because(因为) he plays sports. He runs every day. He runs to his ___①____ in the morning and he runs ____②____ after school in the afternoon. He can run fast. He likes playing soccer, volleyball, tennis, basketball , ping-pong and more. He has three soccer balls, two volleyballs, six tennis rackets, four basketballs and many ping-pong balls. They are in his room. He plays sports with his friends every day. He likes many sports stars and he often watches them on TV. All my classmates say Jack is sporty (爱好体育)。