2000年1月大学英语四级考试真题与答案_第6页

Questions 36 to 40 are based on the following passage:
　　Why does cream go bad faster than butter? Some researchers think they 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.C ream and butter contain pretty much the same substances，so why cream should sou r muchfaster has been a mystery.Both are emulsions - tiny globules(小球)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 and what's in the surround ing liquid，says Brocklehurst，who led the investigation.In cream，fatty globul es drift about in a sea of water.In butter，globules of a watery solution are l ocked away in a sea of fat.The bacteria which make the food go bad prefer to li ve 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 revers ed，the bacteria are locked away in compartments (密封仓) buried dee p 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 wast e products."In butter，you get a self - limiting system which stops the bacteri a growing，"says Brocklehurst.The researchers are already working with food com panies keen to see if their products can be made resistant to bacterial attack t hrough alterations to the food's structure.Brocklehurst believes it will be pos sible 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 faster than butter because bacteria_____ .
　　A) are more evenly distributed in cream
　　B) multiply more easily in cream than is butter
　　C) live on less fat in cream than in butter
　　D) produce less waste in cream t han 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 s alad 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