来源：百度知道 编辑：UC知道 时间：2024/06/23 00:08:44
The Food and Drug Administration has recently proposed severe restrictions on the use of antibiotics to promote the health and growth of meat animals. Medications added to feeds kill many microorganisms but also encourage the appearance of bacterial strains that are resistant to anti-infective drugs. Already, for example, penicillin and the tetracyclines are not as effective therapeutically as they once were. The drug resistance is chiefly conferred by tiny circlets of genes, called plasmids, that can be exchanged between different strains and even different species of bacteria. Plasmids are also one of the two kinds of vehicles (the other being viruses) that molecular biologists depend on when performing gene transplant experiments. Even present guidelines forbid the laboratory use of plasmids bearing genes for resistance to antibiotics. Yet, while congressional debate rages over whether or not to toughen these restrictions on scientists in their laboratories, little congressional att
匆忙一试，所得答案为EABE。不知正确与否
第一题主旨题，由于文章一共就一段，所以要分清段内层次。
首句引入1个proposed restrictions。
第2句开始解释这个proposal的原因----为什么要限制-----Antibiotics的缺陷
然后开始举例证明这1个分论点
第3层是从The drug resistance is...开始，解释这个缺陷产生的原因，引入plasmids这个概念。
然后解释plasmids的作用机理。
第4层从Plasmids are also one of the two kinds of vehicles (the other being viruses) that molecular biologists depend on when performing gene transplant experiments。开始引入了细胞移植实验这个issue.
最后讨论关于 反对--实验---农业practice等的联系。
从脉络可以看出主旨是在评价最近的restrictions。
第二题，细节题。细节题最重要的是理清题目所要求的内容之间的关系。
题目问the exchange of plasmids between different bacteria can results in which of the following。
the exchange of plasmids between different bacteria 是在文章解释plasmids的作用机理的时候出现，这1层文章的目的，就是题目的要求。定位原文，这1层是文章的第3层，The drug resistance is chiefly conferred by tiny circlets of genes, called plasmids。
这层的目的就是为了解释缺陷产生的原因，也就是为什么出现抗药性。所以A是对的。
至于楼主所问之E选项，细胞移植实验，这是在后面谈到plasmids的另外1个作用领域的时候的举例。此
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