it is almost known to all that smoking is bad for people's health.
　　scientific researchs show that smoking can lead to heart disease,cancer and other problem.the world health organization says diseases linked to smoking kill at least two million five-hundred-thousand persons each year.
　　still,many people find it difficult to stop smoking.one reason is that smoking usually becomes a habitual behaviour,and habits,whether good or bad are not easy to be given up.another reason is the effect of nicotine,the substance found in cigarettes works on people somewhat as drugs do.
　　measures have been taken to help people keep away from the harm of smoking. in many cities,smoking is forbidden in public places.the danger of smoking is warned of everywhere.and newspapers are asked not to publish advertisements for cigarettes.
　　world "no tobacco day" is observed every year as the biggest compaign against smoking.