一个物体由静止开始做匀加速直线运动，加速度大小为a₁，经 $\frac{t}{2}$ 时间后，物体的加速度大小变为a₂，又经过t时间恰好回到出发位置，则a₁与a₂的大小之比为（   ）

(不多于3个单词)或括号内单词的正确形式。

    A lecturer was giving a lecture to his students on stress management. He raised a glass of water and asked the audience, “How heavy do you think this glass of water is?” The students' answers ranged from 20g to 500g. It doesn't matter on the absolute ____ (weigh). It depends on how long you hold ____. If I hold it for a minute, it is OK. If I hold it for an hour, I'll have ____ ache in my right arm. If I hold it for a day, you will have to call an ambulance. It's the exact same weight, but the ____ (long) I hold it, the heavier it becomes. If we carry our burdens ____ the time, sooner or later, we won't be able to carry on, the burden ____ (become) increasingly heavier. What you've to do is to put the glass down, rest for a while before holding it up again. We have to put down the burden periodically, so that we can ____ (refresh) and are able to carry on.

    ____ you return home from work tonight, put the burden of work ____. Don't carry it back home. You can pick it up tomorrow. Whatever burdens you're having now on your shoulders, let it down ____ a moment if you can. Life is short, enjoy it!

西方和南方中间的是____。