学习游泳时不应空腹下水。（  ）

如图所示，发射同步卫星的一种程序是：先让卫星进入一个近地的圆轨道，然后在P点点火加速，进入椭圆形转移轨道（该椭圆轨道的近地点为近地轨道上的P，远地点为同步轨道上的Q），到达远地点时再次自动点火加速，进入同步轨道．设卫星在近地圆轨道上运行的速率为v₁，在P点短时间加速后的速率为v₂，沿转移轨道刚到达远地点Q时的速率为v₃，在Q点短时间加速后进入同步轨道后的速率为v₄，则四个速率的大小排列正确的是（   ）

    Andy is 12 years old. He is one of my best f____. He is a top student in Class 6. But he doesn't have a good diet.

    Every morning, he doesn't eat breakfast. It isn't right. I think breakfast is very i____ for him. It helps him start the day w____. He has lots of snacks like chocolates, sweets every day. They make him fat. It's bad for his health. Andy shouldn't eat too many snacks any more. In vegetables and fruits there are many vitamins. But he h____ eating them. These days he doesn't feel good.

    I think he needs to c____ his diet. And he needs to exercise more. I'm sure he'll be better.

下列说法中正确是（   ）