Passage 2

　　An ideal design for a toothbrush has not been invented. Dentists have put forward many different designs over the years and each has its advantages. We all know the problems of trying to clean less accessible areas, where it is difficult to see and space is restricted. In trying to clean the backs of our lower front teeth and our wisdom teeth we have produced toothbrushes with every type of bend in the handles and curve on the surface of the bristles(猪鬃、毛发). Added to this there is the choice of natural bristle or nylon for the heads of the toothbrush.

　　After numerous tests it has been found that there is no difference in effectiveness between the natural and artificial bristle. In fact, dentists are finding more advantages with the nylon toothbrush. Nylon bristle is said to last longer, is more easily cleaned and harbours fewer germs. The individual nylon bristles tend to be more consistent in texture and do not become soft. The bristles, moreover, do not split as is the case with natural bristle.

　　The main advantage of natural bristles appears to be that they are more resilient(有弹性的) when new. Another controversy is the appearance of hard, medium and soft toothbrushes. We are told that certain hard brushes are good for smokers and promote healthy gums. Once again the publicity is misleading, starting with the conception that hardness means a bristle of a tougher substance. This is not so, for a hard toothbrush is one in which the diameter of the bristles is greater, thus making the brush more rigid. This causes problems because the gums are easily injured and the tooth surface is more easily worn away by this type of brush. In fact, too much pressure and the wrong technique with a hard brush can cause much damage to the teeth and gums. As the bristles are thicker, they cannot get into the narrow openings so easily. The only advantage of this type of brush is that it lasts longer. In general, therefore, a hard toothbrush is not recommended unless used with extreme care. It is much more advisable to use a medium or soft bristle toothbrush. They don’t have a very long life, and replacement is necessary as soon as the bristles split or fall out.

　　26. According to the passage, the artificial bristle is _______.

　　A. more effective than the natural one

　　B. less effective than the natural one

　　C. just as effective as the natural one

　　D. firmer and cleaner than the natural one

　　27. Which of the following, according to the passage, is an advantage of the nylon toothbrush?

　　A. The bristles split more easily.

　　B. The bristles are free from germs.

　　C. The bristles always stay firm.

　　D. The bristles last longer.

　　28. A hard brush is _______.

　　A. a brush with hard bristles B. a brush with thick bristles

　　C. good for smokers D. good for the gums

　　29. The wrong technique with a hard brush means _______.

　　A. the wrong use of brush B. too much pressure

　　C. the wrong sort of brush D. the wrong toothbrush

　　30. Which of the following is true according to the passage?

　　A. A hard brush is all right if you use it firmly.

　　B. A medium brush is recommended as the bristles last longer.

　　C. A soft brush will soon need replacing.

　　D. A brush that is a mixture of medium and soft bristles is recommended.