Never try to work when you are very hungry. If you want to do your homework right after school, you may want to eat something before getting to work. ①Always do your homework before you get too tired. Don't wait until very late in the evening, or your homework will seem much harder than it really is.
   If you have more than an hour's work，you should give yourself a break after an hour. On the other hand，② you should work at least half an hour a time without stopping.
   Don't put it off（推迟）until the last minute. If you put off doing your homework，you will have it on your mind，and you won't enjoy your free time so much. If you put it off until the end of the week or until night before a test，you will have too much catching up to do. A little each night, enough to keep up with（跟上）what is happening each day in school，will take the fear out of tests and keep you on top of it.
   Do your homework at the same time every day. This will help you make it a habit. It will make part of your daily work easier to do，and it will make your free time more enjoyable as well.

同学们做红花，第一组做了38朵，第二组做了24朵，第三组做了12朵，总共做了​____朵。

今年5月12日汶川发生强烈地震，党和政府十分关怀灾区人民的生命安危，使用了很多最新科技设备进行救援．

（1）生命探测仪：光学生命探测仪将一根柔软细长的光纤管伸进瓦砾堆中扭动前行，搜救人员利用观察器可以看清瓦砾深处的情况，光沿弯曲的光纤传播是利用了光的____ 原理；

（2）热红外生命探测仪利用感知____ 差异来判断不同的目标，因此在黑暗中也能确定生命体的位置；声波生命探测仪有3～6个“耳朵”﹣﹣声探头，即使幸存者不能说话，只要轻轻敲击使周围物体____ 发出微小声响，就能够被它“听”到，甚至心脏微弱的颤动，它也能探测到．