1. (2019九下·温州竞赛) 阅读理解

    Both seasonal flu, a disease like a very bad cold, and much larger pandemics, like the one caused by H7N9（禽流感） in 2013, are the result of a race between the flu virus  and the immune system which can protect people from illness. Here's how it works.

    Viruses, which cause pandemics, have two important proteins "haemagglutinin(H) and neuraminidase(N).H helps the virus go into a cell .N helps new virus break out of that cell .They are parts of a virus that may be known and dealt with by the immune system

    A flu virus attacks a host cell in order to reproduce itself. But the virus created out of it is quite different now. The virus's genetic material is copied with low fidelity. That difference produces virus which immune system does not always know and deal with immediately. Each year's seasonal virus is therefore a little bit different, and thus requires an updated vaccine to prevent people from getting that disease.

    Pandemics viruses have bigger changes in this process .Many hosts' defences are unprepared for such big changes, which happen three or four times a century .The 1918 pandemics was caused by viruses carrying H1 and N1.Anotber two pandemics in 1957 and 1968 were caused by viruses carrying H2and H3 together with N2.They are numbered by scientists. Much of this change goes on outside humans. A flu is usually from sick binds. Sometimes a bird-flu appears with materiel that enable it to spread among people .The H7N9 is recently worrying scientists in the health center.

    The flu virus sometimes jumps directly from a bird(often a chicken) to a person, but more usually passes through a pig The cells in bird and human are built differently, It means us that the virus needs different sets of material to attack them .Pig cells have features of both so that it can act as a platform in which the virus can fit from one to the other .Even after it has made humans ill, a virus cannot go ca to cause a pandemic unless it also gets the ability to pus easily between people, Luckily, this is something H7N9 has yet to do.

1. （1） The underlined ward "pandemics" in the first paragraph probably is    .

   A . a virus from pigs and chicken B . an animal carrying flu viruses C . a disease passing easily around D . a race inside human body
3. （2） Paragraph 2 is mainly about       .

   A . the harm of viruses. B . the spread of viruses   C . the cause of viruses D . the structure of viruses
5. （3） What can we learn from the passage?

   A . H7N9 can move from person to person easily now B . Flu viruses develop both inside and outside humans. C . Pandemics viruses change very often during a short time. D . Immune system can always keep flu viruses away immediately
7. （4） What is the best title of the passage?

   A . A Serious Disease Worrying Scientists B . A New Effective Way to Prevent Viruses C . Changeable viruses Mind your H and N D . The Important Function of Immune System