单选题What is the main idea of the passage?A Man-smokers live shorter than woman-smokers.B All the deaths in Britain result directly from tobacco smoking.C Smoking is the main killer of babies.D Smoking can give rise to several major diseases.

People have smoked cigarettes for a long time now. The tobacco which is used to make cigarettes was first grown in what is now part of the United States. Christopher Columbus, who discovered America, saw the Indians smoking. Soon the dried leaves were transported to Europe. In the late 1800s, the Turks made cigarettes popular.
Cigarette smoke contains at least two harmful substances, tar and nicotine. Tar, which forms as the tobacco bums, damages the lungs and therefore affects breathing. Nicotine, which is found in the 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 their stomachs. 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 and feet. It plays an important role in increasing smokers′ risk of heart disease and stroke.
Smoking cigarettes is dangerous. Cigarette smoking was the cause of lung cancer and several other deadly diseases.
Tobacco first appeared in ___________.

A.Asia
B.Africa
C.Europe
D.America

Today ,as in every other day of the year ,more than 3000 U.S. adlescents will smoke their first cigarette on their way to becoming regular smokers as adults. During their lifetime,it can be expected that of these 3000 about 23 will be murdered,30 will die in traffic accidents, and nearly 750 will be killed by a smoking-related disease. The number of deaths attributed to cigarette smoking outweithts all other factors, whether voluntary or involuntary, as a cause of death.
Since the late 1970s, when daily smoking among high school seniors reached 30 precent , smoking rates among youth have declined . While the decline is impressive ,several important issues must be raised.
First, in the past several years,smoking rates among youth have declined very little. Second,in the late 1970s ,smoking among male high school seniors exceeded that among female by nearly 10 percent . The statistic is reversing.Third ,several recent studies have indicate high school dropouts have excessively high smoking rates, as much as 75 percent .
Finally, thouth significant declines in adolescent smoking have occurred in the past decade,no definite reasons for the decline exist. Within this context,the Naional Cancer Instiute (NCI) began its current effort to determine the most effecive measures to reduce smoking levesl among youth.
By "dropout" the author means___.

a.students who failed the examination
b.students who left school
c.students who lost their way
d.students who were driven out of school

People have smoked cigarettes for a long time now. The tobacco which is used to make cigarettes was first grown in what is now part of the United States. Christopher Columbus, who discovered America, saw the Indians smoking. Soon the dried leaves were transported to Europe. In the late 1800s, the Turks made cigarettes popular.
Cigarette smoke contains at least two harmful substances, tar and nicotine. Tar, which forms as the tobacco bums, damages the lungs and therefore affects breathing. Nicotine, which is found in the 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 their stomachs. 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 and feet. It plays an important role in increasing smokers′ risk of heart disease and stroke.
Smoking cigarettes is dangerous. Cigarette smoking was the cause of lung cancer and several other deadly diseases.
What′s the main idea of this passage?

A.Where did cigarettes come from?
B.The effect of smoking on your body.
C.How to smoke is healthy?
D.Who is the first smoker?

People have smoked cigarettes for a long time now. The tobacco which is used to make cigarettes was first grown in what is now part of the United States. Christopher Columbus, who discovered America, saw the Indians smoking. Soon the dried leaves were transported to Europe. In the late 1800s, the Turks made cigarettes popular.
Cigarette smoke contains at least two harmful substances, tar and nicotine. Tar, which forms as the tobacco bums, damages the lungs and therefore affects breathing. Nicotine, which is found in the 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 their stomachs. 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 and feet. It plays an important role in increasing smokers′ risk of heart disease and stroke.
Smoking cigarettes is dangerous. Cigarette smoking was the cause of lung cancer and several other deadly diseases.
What is the main purpose of the first paragraph?

A.To tell us the bad effects caused by smoking cigarettes.
B.To introduce the history of smoking.
C.To let us know what the cigarettes are made from.
D.To tell the readers that Columbus found the Indians smoking.

Today ,as in every other day of the year ,more than 3000 U.S. adlescents will smoke their first cigarette on their way to becoming regular smokers as adults. During their lifetime,it can be expected that of these 3000 about 23 will be murdered,30 will die in traffic accidents, and nearly 750 will be killed by a smoking-related disease. The number of deaths attributed to cigarette smoking outweithts all other factors, whether voluntary or involuntary, as a cause of death.
Since the late 1970s, when daily smoking among high school seniors reached 30 precent , smoking rates among youth have declined . While the decline is impressive ,several important issues must be raised.
First, in the past several years,smoking rates among youth have declined very little. Second,in the late 1970s ,smoking among male high school seniors exceeded that among female by nearly 10 percent . The statistic is reversing.Third ,several recent studies have indicate high school dropouts have excessively high smoking rates, as much as 75 percent .
Finally, thouth significant declines in adolescent smoking have occurred in the past decade,no definite reasons for the decline exist. Within this context,the Naional Cancer Instiute (NCI) began its current effort to determine the most effecive measures to reduce smoking levesl among youth.
According to the author, the deaths among youth are mainly caused by _____.

a.traffic accidents
b.smoking-related desease
c.murder
d.all of these

Today ,as in every other day of the year ,more than 3000 U.S. adlescents will smoke their first cigarette on their way to becoming regular smokers as adults. During their lifetime,it can be expected that of these 3000 about 23 will be murdered,30 will die in traffic accidents, and nearly 750 will be killed by a smoking-related disease. The number of deaths attributed to cigarette smoking outweithts all other factors, whether voluntary or involuntary, as a cause of death.
Since the late 1970s, when daily smoking among high school seniors reached 30 precent , smoking rates among youth have declined . While the decline is impressive ,several important issues must be raised.
First, in the past several years,smoking rates among youth have declined very little. Second,in the late 1970s ,smoking among male high school seniors exceeded that among female by nearly 10 percent . The statistic is reversing.Third ,several recent studies have indicate high school dropouts have excessively high smoking rates, as much as 75 percent .
Finally, thouth significant declines in adolescent smoking have occurred in the past decade,no definite reasons for the decline exist. Within this context,the Naional Cancer Instiute (NCI) began its current effort to determine the most effecive measures to reduce smoking levesl among youth.
What is implied but not stated by the author is that ________.

a.smoking rates among youth have declined very little
b.there are now more female than male smokers among high school seniors
c.high smoking rates are due to the incease in wealth
d.smoking at high school are from low socio-economic backgrounds