網校每日一練免費在線測試系統(tǒng)將為所有學員免費提供練習題，所有學員登錄成功之后即可免費練習。如有疑問可以到答疑板與專家進行交流，24小時之內即可得到滿意答復。歡迎大家積極參與！

　　補全短文

　　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 health.________.They discovered that even nonsmokers had unhealthy amounts of these toxic (有毒的) chemicals in their bodies.

　　A、The Gilsons have been married for 35 years.

　　B、Recently, though, scientists changed their opinion after they studied a large group of nonsmokers.

　　C、We cannot avoid secondhand smoke in restaurants.

　　D、In the United States, nine million children under the age of five live in homes with at least one smoker.

　　【正確答案】 B

　　【答案解析】前一句講的是科學家們過去對二手煙的看法，接下來應選表示他們改變觀點的句子，因為下一句表明他們所持的觀點已與過去截然不同。