单选题：阅读下文，回答题。The Dangers of Secondhand SmokeMost people know t

阅读下文，回答题。
The Dangers of Secondhand Smoke
Most people know that cigarette smoking is harmful to their health．Scientific research shows that it causes many kinds of diseases．In fact，many people who smoke get lung cancer However，Edward Gilson has lung cancer，and he has never smoked cigarettes．He lives with his wife，Evelyn，who has smoked about a pack of cigarettes a day throughout their marriage．
_ 1__ No one knows for sure why Mr．Gilson has lung cancer．Nevertheless，doctors believe that secondhand smoke may cause lung cancer in people who do not smoke because nonsmokers often breathe in the smoke from other people’S cigarettes． __2___The US Environmental Protection Agency reports that about 53，000 people die in the United States each year as a result of exposure to secondhand smoke．
The smoke that comes from a lit cigarette contains many different poisonous chemicals．In the past．scientists did not think that these chemicals could harm a nonsmoker’S healtll．
__3 _They discovered that even nonsmokers had unhealthy amounts of these toxic(有毒的)chemicals in their bodies．As a matter of fact，almost all of US breathe tobacco smoke at times．whether we realize it or not．For example，we cannot avoid secondhand smoke in restaurants，hotels and other public places．Even though many public places have nonsmoking areas，smoke flows in from the areas where smoking is permitted．It is even harder for children to avoid secondhand smoke．__4_ Research shows that children who are exposed to secondhand smoke are sick more often than children who live in homes where no one smokes and that the children of smokers are more than twice as likely to develop lung cancer when they are adults as are children of nonsmokers．The risk is even higher for children who live in homes where both parents smoke．
People are becoming very aware of the dangers of secondhand smoke． __5__
请在1处填写正确答案。 A．Recently，though，scientists changed their opinion after they studied a large group of nonsmokers．
B．The Gilsons have been married for 35 years．
C．This smoke is called secondhand smoke．
D．However，secondhand smoke is dangerous to all people，old or young．
E．As a result．they have passed Iaws which p rohibit people from smoking in many public places．
F．In the United States．nine million children under the age of five live in homes with at Ieast one smoker