B People have smoked tobacco for centuries, and the harmful effects of tobacco smoke have been seen as controversial since at least the 16th century when European explorers introduced tobacco to North America. Cigarette, in fact, typically contains more than 4,700 chemical compounds, 43 of which are believed to cause cancer. Compounds such as tar and sulphur do most of the harm, whilst a poisonous compound known as nicotine makes smoking very difficult to give up. In 1964, a committee of doctors and scientists in the United States of America concluded that nearly all forms of lung cancer were caused by the negative effects of smoking. They also reported, however, that smoking leads to many other diseases, such as chronic bronchitis and emphysema(disease of the lung). A more worrying report, however, argued that as many as 50,000 people die each year in America from the effects of passive smoking( breathing in other people’s smoke). Young children are vulnerable because it is believed restrictions in oxygen supplies lead to stunted growth. But pregnant women are especially susceptible to this type of exposure because the smoke prevents oxygen supplies in the blood stream reaching the foetus, thereby inhibiting natural development. Smoking has thus been deemed more harmful than the effects of alcohol and has led to the becoming of smoking in public-parks in some ares. The most recent research carried out in the UK, however, suggest that if young girls beg in smoking daring puberty(early teenage years), which is common amongst teenagers in Europe, they are far more likely to contract because cancer as they grow older. Moreover, whilst the dangers of contracting diseases such as bronchitis and even lung cancer never let up. Instead it remains with the girl for the reminder of her natural life. These,and other findings,have promoted many European countries to launch a no smoking campaign in schools,aimed at making young,vulnerable adolescents,who are in a transition period between children and adulthood,aware of the dangers of smoking with the adage that prevention is better than cure. Why is smoking addictive Because it contains ______.