2. 外语
  3. The term "virus" is derived from the Latin word for poison, or slime. It was originally applied to the noxious stench emanating

The term "virus" is derived from the Latin word for poison, or slime. It was originally applied to the noxious stench emanating

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问题      The term "virus" is derived from the Latin word for poison, or slime. It was originally applied to the noxious stench emanating from swamps that was thought to cause a variety of diseases in the centuries before microbes were discovered and specifically linked to illness. But it was not until almost the end of the nineteenth century that a true virus was proven to be the cause of a disease.
     The nature of viruses made them impossible to detect for many years, even after bacteria had been discovered and studied. Not only are viruses too small to be seen with a light microscope, they also cannot be detected through their biological activity, except as it occurs in conjunction with other organisms. In fact, viruses show no traces of biological activity by themselves. Unlike bacteria, they are not living agents in the strictest sense. Viruses are very simple pieces of organic material composed only nucleic acid, either DNA or RNA, enclosed in a coat of, protein made up of simple structural units. They are parasites, requiring human, animal or plant cells to live. The virus replicates by attaching to a cell and injecting its nucleic acid; once inside the cell, the DNA or RNA that contains the virus’ genetic information takes over the cell’s biological machinery, and the cell begins to manufacture viral protein rather than its own.
Which of the following is the best title for the passage?
选项 A、New Developments in Viral Research.
B、Exploring the Causes of Disease.
C、DNA: Nature’s Building Block.
D、Understanding Viruses.
答案D
解析 本题考查主旨大意。从文章可以看出，本文主要叙述了有关病毒特性的一些知识，有助于人们对病毒的了解。因此选项D 可作为文章标题。而A ，B ，C 在文中虽然提到，但不是本文的主要内容。
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