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  When Oakland High School in California moved into a new building．the students and teachers noticed a strong smell．Then almost half of the students began to have a headache and a cough．Experts(专家)came to find the cause of the sickness．Finally，they discovered that the air in the building was not safe to breathe．They were surprised to find out that the desks and chairs in the school library caused the trouble．These desks and chairs were made of particleboards(合成板)．This kind of board is cheap．It is made of very small pieces of wood held together with a chemical(化学物质)．This is just one example of a modem problem that is most common in cities—indoor air pollution(污染)．

  People have worried about air pollution for many years，and the government has spent lots of money trying to clean up the air of big cities．But now we found that we are still breathing unhealthy air．A study shows：Indoor air pollution is almost two to five times(倍)worse than outside pollution．So remember to open the windows and don’t stay too long in modern buildings with windows closed．

(  )51．Many students and teachers ________ after they moved into the new building．

  A. were very happy and excited       B. didn’t feel well  C．felt tired because of hard work

(  )52．The experts came to Oakland High School for ________ ．

  A．staying with the sick students and teachers       B．taking away the desks and chairs

  C．finding the cause of the illness

(  )53．Which of the following is NOT true according to the passage?

  A．The indoor air pollution is common in cities．

B．We needn’t worry about the outside pollution．

  C．The air in this school library was not safe to breathe．

(  )54．A study shows that indoor air pollution is ________ ．

  A. even worse than the outside pollution             B．not so bad as outside pollution

  C．the only problem to worry about

(  )55．What’s the main idea of the passage?

  A. Never move into a new building．  B. We shouldn’t buy cheap desks and chairs．

  C．The indoor air pollution is a big and common problem．