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 (小球體) 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 (隔倉室) buried deep in the sea of fat. Trapped in this way, individual colonies cannot spread and rapidly run out of nutrients (養料). They also slowly poison themselves with their waste products. “In butter, you get a self-limiting system which stops the bacteria growing,” says Brocklehurst.

　　The researchers are already working with food companies keen to see if their products can be made resistant to bacterial attack through alterations to the food’s structure. Brocklehurst believes it will be possible to make the emulsions used in salad cream, for instance, more like that in butter. The key will be to do this while keeping the salad cream liquid and not turning it into a solid lump.

　　36. The significance of Brocklehurst’s research is that ________.

　　A) it suggested a way to keep some foods fresh without preservatives

　　B) it discovered tiny globules in both cream and butter

　　C) it revealed the secret of how bacteria multiply in cream and butter

　　D) it found that cream and butter share the same chemical composition

　　37. According to the researchers, cream sours fast than butter because bacteria ________.

　　A) are more evenly distributed in cream

　　B) multiply more easily in cream than in butter

　　C) live on less fat in cream than in butter

　　D) produce less waste in cream than in butter

　　38. According to Brocklehurst, we can keep cream fresh by ________.

　　A) removing its fat

　　B) killing the bacteria

　　C) reducing its water content

　　D) altering its structure

　　39. The word “colonies” (Line 2, Para. 4) refers to ________.

　　A) tiny globules

　　B) watery regions

　　C) bacteria communities

　　D) little compartments

　　40. Commercial application of the research finding will be possible if salad cream can be made resistant to bacterial attack ________.

　　A) by varying its chemical composition

　　B) by turning it into a solid lump

　　C) while keeping its structure unchanged

　　D) while retaining its liquid form

　　Unit 2

　　21. B 22. A 23. B 24.D 25. C

　　26. A 27. C 28. C 29.A 30. B

　　31. D 32. B 33.C 34. D 35. A

　　36. A 37. B 38. D 39.C 40. D

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