39. One way to prevent fires at home is to _________.

    A. leave stoves in the middle of the rooms

B. dry clothes near stoves

    C. tell children to stay away from fire

D. smoke away from fires

(B)

Through all of human history, rats have been a curse and a plague (祸害) to people. They eat or spoil crops of grain and rice before they can be harvested or while they are in storage. In India, where millions of people go hungry, there are ten times as many rats as people. Rats devour half of the available food. Rats will also attack birds and animals, from flogs and chicks to geese and young calves. They have even destroyed dams and buildings by making holes through or under them. Sometimes they cause fires by chewing on electrical wiring.

   The most terrible destruction caused by rats, however, has come from the diseases they carry. In the fourteenth century, rats caused the death of one-third of the world’s human population by transmitting bubonic plague (淋巴腺鼠疫). This dreadful outbreak also called the Black Plague, ravaged (严重损坏) Europe for years.

   Ironically, it is in fighting diseases that rats have been most useful to humanity. The bodies of rats, though quite different from those of humans, have certain basic structural similarities. So thousands of specially bred rats are used in research laboratories every year to test medicines that can possibly be used to prolong and improve human life. As might be expected, some laboratory rats are even used to test new procedures and methods for eliminating their cousins - the wild rats.

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