题干

夏天,做熟的食品为什么很快就会变质呢,原来,做熟的食品里生出了无数的细菌。食品中的这些细菌是从哪里来呢?是有食品自然产生的,还是来自空气?对此,法国生物学家巴斯德进行了认真的研究。

巴斯德把新鲜、清澈的肉汤分别装入甲、乙两个玻璃瓶里,然后把甲瓶的瓶颈烧软,并拉成鹅颈似的弯曲细长的形状,把乙瓶的瓶口敞开。随后,他再次煮沸瓶内肉汤,然后静置观察。

观察发现,乙瓶内的肉汤很快就腐败变质了;而甲瓶中的肉汤尽管通过弯曲细长的瓶颈可与外界相通,在较长时间内肉汤仍然保持无细菌,不变质。通过实验,巴斯德认为,纯净的肉汤是永远不会自然生出细菌的,使肉汤腐败变质的细菌来自空气。

据此完成下列各题。

上一题 下一题 0.0难度 选择题 更新时间:2020-01-19 11:04:20

答案(点此获取答案解析)

同类题1

阅读理解

Wilderness

    “In wilderness(荒野) is the preservation of the world.” This is a famous saying from a writer regarded as one of the fathers of environmentalism. The frequency with which it is borrowed mirrors a heated debate on environmental protection: whether to place wilderness at the heart of what is to be preserved.  

     As John Sauven of Greenpeace UK points out, there is a strong appeal in images of the wild, the untouched; more than anything else, they speak of the nature that many people value most dearly. The urge to leave the subject of such images untouched is strong, and the danger exploitation(开发) brings to such landscapes(景观) is real. Some of these wildernesses also perform functions that humans need—the rainforests, for example, store carbon in vast quantities. To Mr.Sauven, these ”ecosystem services” far outweigh the gains from exploitation.

    Lee Lane, a visiting fellow at the Hudson Institute, takes the opposing view. He acknowledges that wildernesses do provide useful services, such as water conservation. But that is not, he argues, a reason to avoid all human presence, or indeed commercial and industrial exploitation. There are ever more people on the Earth, and they reasonably and rightfully want to have better lives, rather than merely struggle for survival. While the ways of using resources have improved, there is still a growing need for raw materials, and some wildernesses contain them in abundance. If they can be tapped without reducing the services those wildernesses provide, the argument goes, there is no further reason not to do so. Being untouched is not, in itself, a characteristic worth valuing above all others.

    I look forwards to seeing these views taken further, and to their being challenged by the other participants. One challenge that suggests itself to me is that both cases need to take on the question of spiritual value a little more directly. And there is a practical question as to whether wildernesses can be exploited without harm.

    This is a topic that calls for not only free expression of feelings, but also the guidance of reason. What position wilderness should enjoy in the preservation of the world obviously deserves much more serious thinking.