C. In families of New York, Philadelphia, and Baltimore.

　　D. In fresh meat, fish and butter by city dealers.

　　47. What was essential to to make an icebox efficient according to the passage?

　　A. Keeping the ice from melting

　　B. Knowledge of the physics of heat.

　　C. Balance of insulation and circulation

　　D. Making efforts to reduce the use of ice

　　48. The second paragraph is mainly about_____

　　A. the deveopment of icebox

　　B. the theoretical foundation of icebox

　　C. the wrong ideas about icebox

　　D. the way of using icebox

　　49. What can we infer from the text?

　　A. Thomas Moore is the inventor of modern fridge

　　B. The butter produced by Thomas Moored is better in quality than other famers’

　　C. Knowledge of the physics of heat plays an important part in inventing a good icebox

　　D. Before 1880, most of the sold ice was used for family use.

　　50. Without an ice box, farmers had to go to the market at night ________.

　　A. to sell their produce at high price

　　B. to go home earlier

　　C. to keep their produce fresh

　　D. to win more customers than their competitors

　　D

　　Dr. Jack M. Gwaltney, Jr. a professor at the University of Virginia School of Medicine, infected six student volunteers with virus, the most common cause of colds. A few days later, when they were coughing and sneezing, he gathered 37 more people and divided them into three groups. Group 1 members spent three days and nights in the same room with one of the infected students, separated by a screen so they couldn't touch one another. Group 2 sat around a table while an infected volunteer talked, coughed and sang to them. Group 3 held hands with an infected student for ten seconds, and then touched their own noses or eyes.

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