最新大学英语四级阅读考试过关必备的训练(1)_大学英语阅读

最新大学英语四级阅读考试过关必备的训练(1)

　　A) the attractiveness of its name and route was effectively advertised

　　B) it provided an exciting travel experience

　　C) its passengers could enjoy the great western outdoors

　　D) it was widely advertised in newspapers and magazines in Chicago and Seattle

　　Passage Four

　　Questions 36 to 40 are based on the following passage.

　　Why does cram go bad faster than butter? Some researchers think they have the answer, and it comes down to the structure of the food, not its chemical composition a finding

　　that could help rid some processed foods of chemical preservatives.

　　Cream and butter contain pretty much the same substances, so why cream should sour much faster has been a mystery. Both are emulsions tiny globules of one liquid evenly distributed throughout another. The difference lies in what s in the globules and what s in the surrounding liquid, says Brocklehurst, who led the investigation.

　　In cream, fatty globules drift about in a sea of water. In butter, globules of a watery solution are locked away in a sea of fat. The bacteria which make the food go bad prefer to live in the watery regions of the mixture. This means that in cream, the bacteria are free to grow throughout the mixture, he says.

　　When the situation is reversed, the bacteria are locked away in compartments buried deep in the sea of fat. Trapped in this way, individual colonies cannot spread and rapidly run out of nutrients . They also slowly poison themselves with their waste products. In butter, you get a self-limiting system which stops the bacteria growing, says Brocklehurst.