2014年12月大学英语四级考试预测试卷2_第6页

　　听力填空题

　　26、听材料，回答下列各题：

　　Directions：In this section.you will hear a passage three times.When the passage is read for the first time,you should listen carefully for its general idea.When the passage is read for the second time,you arerequired to fill in the blanks with the exact words you have just heard.Finally,when the passage is read for the third time,you should check what you have written.

　　Why does cream go bad faster than butter?Some researchers think that 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 much the same(26)______，so why cream should sour much faster has been a(27)______.Both are emulsions—tiny globules of one liquid evenly(28)______throughout another.The difference lies in what’s in the globules and what’s in the surrounding.In cream，fatty globules(29)______about in a sea of water.In butter,globules of a watery(30)______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(31)______.This means that in cream，the bacteria are flee to grow throughout the mixture.When the situation is(32)______，the bacteria are locked away in(33)______buried deep in the sea of fat.

　　Trapped in this way,(34)______colonies cannot spread and rapidly run out of nutrients.They also slowly poison themselves with their waste products.

　　In butter，there is a self-limiting system which stops the bacteria growing.The researchers are already working with food companies keen to see if their products can be made(35)______ to bacterial aRack through alterations to the food’s structure.They believe that it will be possible to make the emulsions used in salad cream，for instance，more like that in buRer.The key will be to do this while keeping the salad cream liquid and not turning it into a solid lump.

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