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

admin2010-07-06  60
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.
Before microbes were discovered it was believed that some diseases were caused by
选项 A、germ-carrying insects.
B、certain strains of bacteria.
C、foul odors released from swamps.
D、slimy creatures living near swamps.
答案C
解析 本题考查细节辨析。文中提到，在细菌被发现之前，认为沼泽地发出的有毒恶臭会引起多种疾病的观点流传了几个世纪。而文中并没说疾病是由A 携带微生物的昆虫，B 某些细菌；D 生活在沼泽附近的粘质生物，等原因引起的。故C 正确。
转载请注明原文地址:https://www.kaotiyun.com/show/DPDd777K
本试题收录于： 公共英语四级笔试题库公共英语（PETS）分类
0

公共英语四级笔试

公共英语（PETS）

相关试题推荐
随机试题
最新回复(0)