题目内容：
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A．Recently, 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 laws which prohibit 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 least one smoker.
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答案解析：