辨认主题句

Read the following paragraph and choose the best topic sentence from the four options that follow.
    While some adults decide to give up smoking, many teenagers begin to smoke cigarettes. They think smoking can help them to be more manly or fresh-minded. However, smoking is harmful to the smokers themselves. If you smoke, the cigarette can make your heart beat faster, shoot your blood pressure up, replace oxygen in your blood with carbon monoxide (一氧化碳) and leave cancer-causing substances in your body. According to a recent WHO report, 95% of those who suffer from lung cancer are smokers. As for heart disease, the risk of death is 2 to 3 times as great in smokers as in non-smokers. Smoking also brings great harm to the non-smokers in public places. If someone smokes in the waiting room of a railway station, twenty or even more people around him will be affected by the harmful substances carried in the smoke. We should completely ban smoking in public places.