根据以下材料，回答题 People have smoked cigarettes for a longtime now. The tobacco which is used to make cigarettes was first grown in whatis now part of the United States. Christopher Columbus, who discovered America,saw the Indians smoking. Soon the dried leaves were transported to Europe. In thelate 1800s, the Turks made cigarettes popular. Cigarette smoke contains at least twoharmful substances, tar and nicotine. Tar, which forms as the tobacco burns,damages the lungs and therefore affects breathing. Nicotine, which is found inthe leaves, causes the heart to beat faster and increases the breathing rate.Nicotine in large can kill a person by stopping a person′s breathing muscles.Smokers usually take in small amounts that the body can quickly break down. Nicotine can make new smokers feel dizzy (头晕) or sick to theirstomachs. The heart rate for young smokers increases 2 to 3 beats per minute.Nicotine also lowers skin temperature and reduces blood flow in the legs andfeet. It plays an important role in increasing smokers′ risk of heart disease andstroke. Smoking cigarettes is dangerous. Cigarettesmoking was the cause of lung cancer and several other deadly diseases. ______doesn′t make one′s heart beat asusual.查看材料
A.Tar B.Nicotine C.Lung disease D.Leave