没有空气我们就不能活，......请以fresh air为话题，写一篇短文。

　　提示词：villagers,more healthy,than,towns,air,fresh,all day in the fields,breathing fresh clean air,cities,full of smoke,dust,diseasepoeple in villages are healthier than people in towns. that is because the air in villages is very fresh. farmers are working all day in the fields, breathing fresh clean air. but there are too many factories in cities. they produce more and more harmful gases. at last, cities are full of smoke. and theres many dust in cities,too. it may cause a disease. so fresh air is very important to the people in cities. we need fresh air. so please dont pollute the air!