______（48)A.Recently though scientists changed th
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______（48)
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 second-hand smoke.
D.However,second-hand 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：A
前面一句讲的是过去科学家们认为这些化学物质不会伤害一个不吸烟者的健康。后面一句讲的是研究发现甚至是不吸烟者体内也有大量的有毒物质。此处应表示他们改变了看法并对此做了研究调查。故选A