During the day we work and play, and at night we sleep. Our bodies rest while we are 1. In the morning we are ready2 again. Our bodies grow 3 while we are asleep. Children who are tired usually 4 sleep. We can get better at our lessons 5 we have had plenty of rest. Boys and girls who are eight or nine years old need ten hours of sleep every night. Our bodies need plenty of 6 when we sleep. If we do not get enough fresh air, we 7 tired when we wake up. While in bed we must not cover our 8. Our lungs(肺) need to get enough fresh air. If we 9 our windows at night, we can have plenty of fresh air. Cool air is better than warm air. Boys and girls who want to be 10 must get plenty of sleep.

食醋是一种能增强食品酸味的调味剂，与我们生活密切相关．根据所学知识回答：

消化系统由消化管和消化腺组成，消化腺分泌消化液，但并不是所有的消化液都含消化酶。（判断对错）

质量为m的小球在竖直平面内的圆管轨道内运动，小球的直径略小于圆管的直径，如图所示．已知小球以速度v通过最高点时对圆管的外壁的压力大小恰好为mg，则小球以速度 $\frac{v}{2}$ 通过圆管的最高点时（   ）