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There are over 4.000 ... in the tobacco smoke. Most of them are extremely ... to humans. The harmful chemicals have been found in the cigarettes including carbon monoxide, nitrates, ammonia, hydrogen cyanide, sulphur compounds, nitrosamines, hydrocarbons, vinyl chloride, etc. These chemicals ... together and form a sticky tar. The smell and colour of the cigarette are ... by the tar. In addition, this tar ... to skin, lungs and ... .