题干

某些寄生虫靠不同方法在具有免疫力的人体内生存,称为免疫脱逃作用,如非洲睡眠病原虫.病人感染该寄生虫并出现病症时,血液中的虫数会按着一周左右的周期而波动,每一次波动中,新的虫体都具有新的表面抗原,虽然宿主会再对新的表面抗原产生新的抗体来对抗,但在歼灭虫体之前,寄生虫表面的抗原又改变了,因此使用传统方法制备疫苗来预防感染的做法都失败了.请根据上文判断下列说法错误的是(   )

A:寄生虫细胞表面抗原的化学本质可能是糖蛋白

B:由于病人体内新抗体产生的速度总是慢于虫体表面抗原的改变的速度,因此虫体可以有效脱逃抗体的消灭

C:人在患某些寄生虫病治愈后,今后还有可能再患此病

D:用传统方法制备疫苗来预防感染的做法都失败的原因是体内产生的抗体浓度不够

上一题 下一题 0.0难度 选择题 更新时间:2015-12-08 04:08:35

答案(点此获取答案解析)

D

同类题3

阅读理解

    Increasingly, over the past ten years, people-especially young people have become aware of the need to change their eating habits, because much of the food they eat, particularly processed food, is not good for the health. Consequently, there has been a growing interest in natural foods: foods which do not contain chemical additives and which have not been affected by chemical fertilizers(化肥)widely used in farming today.

    Natural foods, for example, are vegetables, fruit and grain which have been grown in soil that is rich in organic matter. In simple terms, this means that the soil has been nourished by unused vegetable matter, which provides it with essential vitamins and minerals. This in itself is a natural process compared with the use of chemicals and fertilizers, the main purpose of which is to increase the amount but not the quality of foods grown in commercial farming areas.

    Natural foods also include animals which have been allowed to feed and move freely in healthy pastures(生活状况). Compare this with what happens in the mass production of poultry(家禽): there are battery farms, for example, where thousands of chickens live crowded together in one building and are fed on food which is little than rubbish. Chickens kept in this way are not only tasteless as food; they also produce eggs which lack important vitamins.

    There are other aspects of healthy eating which are now receiving increasing attention from experts in diet. Take, for example, the question of sugar. This is actually a nonessential food! It is not that sugar is harmful in itself. But it does seem to be additive: the quantity we use has grown steadily and in Britain today each person consumes an average of 200 pounds a year! Yet all it does is provide us with energy, in the form of calories. There are no vitamins in it, no minerals and no fibre.