尺规作图作$\angle AOB$的平分线方法如下：以$O$为圆心，任意长为半径画弧交$OA$、$OB$于$C$、$D$，再分别以点$C$、$D$为圆心，以大于$\frac{1}{2}CD$长为半径画弧，两弧交于点$P$，作射线$OP$，由作法得△OCP≌△ODP的根据是（   ）
             

某工厂原来用氢氧化钠溶液中和所排废水中的硫酸，现改用氢氧化钾溶液中和以得到钾肥，若氢氧化钾溶液的溶质质量分数与原来氢氧化钠溶液的溶质质量分数相同，则此时碱流量阀调节的方法是（　　）

    There is an old English saying. It tells us that we must go to bed early and get up early in the morning. Then we shall be healthy. We shall also be rich and clever. This is true. The body must have enough sleep to be healthy. Children of young age should have ten hours' sleep every night. Children who do not have enough sleep cannot do their work well and they may not be healthy.

    The body also needs exercise. Walking, running, jumping and playing games are all exercise. Exercise keeps the body strong.

    Exercise also helps the blood to move around inside the body. It is very important. Our blood moves to all parts of our body. The head also needs blood. Exercise helps us to think better.