因为一年有12个月份，《百科知识》月刊每本定价4.50元,所以:

4.5X12=54（元）

答：小明打算订阅一年,要花54元。

急需百科知识竞赛主持语...在线等!悬赏50分

Global Shortage of Fresh Water People often think that water will never be used up.There is plenty of water,suc h as rain,water from the rivers and wells,It seems as if water is always availab le around us and we never have to worry about water shortage. In fact water is rather limited on the earth.With the rapid increase of populati on and fast development of industries,water is more needed than before.At the sa me time,a large amount of water has been polluted and wasted every day.Some big cities in China are facing the problem of water shortage already.There,water sup ly is controlled and industry has been restrained. What should we do about the water shortage?I think,first,the people should be ma de aware of the real situation about the water.Everyone should consciously save on water and certain law should be made that no water will be polluted.We have t o protect the existing water resources and develop new ones.In this way Ibelieve that our cities will be thirsty for water in the future. Today, pollution has become a very serious problem. All forms of pollution do harm to man and animals, such as air pollution, water pollution, soil pollution and so on. Generally speaking, Pollution mainly comes from factories. Each day, chemicals in the smoke from factories cause a lot of damage. Water pollution is also caused by waste from factories. All of these can do harm to people's health. Now people have done something to prevent pollution, but the situation is still serious; we hope scientists will find some new methods to solve this problem. Nowadays, the environmental protection is becoming one of the most important issues in the world. Being one of the members of our society, what shall we do to protect the environment? First, stop using plastic bags, boxe