human brain is the most complex and intelligent mechanism in the world. it is the major factor that distinguishes man from animals. with our brain we get to know the world and make a good use of the world to our benefit.
our brain is a product of constant use through millions of years. other things can be used up, but used properly, our brain can never be exhausted. in fact, the more we use it, the more capable and efficient it will become. excessive use of the brain, however, will causea lot of problems. so it is useful to know how to use our brain wisely.
first, handwork or physical labor is good exercise as well as rest for our brain. doing handwork and brain work alternatively can help develop both our brain and hands. secondly, we should avoid doing brainwork for long hours on end. the brain, though 3% of the body weight, when at work, consumes 20% of the oxygen carried by 16% of the blood in circulation. a long period of brainwork may cause, through lack of bodily activity, slow blood circulation and inadequate oxygen supply to the brain, resulting in inefficiency and possible damage to the brain.
来源：作文地带整理。
