Unit1 语篇练习-2021-2022学年高中英语人教版（2019）选择性必修第一册

语篇练习 一、阅读理解 　　阅读下列短文,从每题所给的A、B、C、D四个选项中选出最佳选项。 　　 A 　　Fever, coughing...most of us at one time or anotherhave had these symptoms. What causes them? 　　In fact, many diseases are caused by viruses, includingsome deadly ones like AIDS, SARS and COVID-19, alsoknown as the novel coronavirus pneumonia.What are viruses? How can viruses cause so muchtrouble? Viruses are very small particles which areabout one millionth of an inch long. Unlike human cells orbacteria, viruses aren't living organisms-they can'treproduce on their own. Instead. they invade the cells ofliving organisms to reproduce, spread and take over.Viruses can infect every living thing-from plants andanimal down to the smallest bacteria. For this reason, theyare always a potential danger to humans.Viruses lie around our environment all of the time,waiting for a host cell to come along. They can enter ourbodies by the nose, mouth, eyes or breaks in the skin. Onceinside, they try to find a host