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4、Nuclear power's（核能的） danger to health, safety, and even life itself can be described in one word; radiation（輻射）．

    Nuclear radiation has a certain mystery about it, partly because it cannot be detected （探測） by human senses．It can't be seen or heard, or touched or tasted, even though it may be all around us．There are other things like that．For example, radio waves are all around us but we can't detect them, sense them, without a radio receiver．Similarly, we can't sense radioactivity without a radiation detector．But unlike common radio waves, nuclear radiation is not harmless to human beings and other living things．

    At very high levels, radiation can kill an animal or human being outright （全部地） by killing masses of cells （細胞） in important organs （器官）．But even the lowest levels can do serious damage．There is no level of radiation that is completely safe．If the radiation does not hit anything important, the damage may not be significant．This is the case when only a few cells are hit, and if they are killed outright．Your body will replace the dead cells with healthy ones．But if the few cells are only damaged, and if they reproduce themselves, you may be in trouble．They reproduce themselves in an unusual way．They can grow into cancer．Sometimes this does not show up for many years．

   This is another reason for some of the mystery about nuclear radiation．Serious damage can be done without the knowledge of the person at the time that damage has occurred．A person can be irradiated（放射治療） and feel fine, then die of cancer five, ten, or twenty years later as a result．Or a child can be born weak or easy to get serious illness as a result of radiation absorbed by its grandparents．

   Radiation can hurt us．We must know the truth．

1．According to the passage, the danger of nuclear power lies in __________．

       A．nuclear mystery                                 B．radiation detection

       C．radiation level                                      D．nuclear radiation

2．Radiation can lead to serious results even at the lowest level ________．

       A．when it kills few cells 

       B．if it damages few cells

       C．though the damaged cells can repair themselves

       D．unless the damaged cells can reproduce themselves

3．Radiation can hurt us in the way that it can _____．

      A．kill large numbers of cells in main organs so as to cause death immediately

      B．damage cells which may grow into cancer years later

       C．a(chǎn)ffect the healthy growth of our younger generation

       D．lead to all of the above results

4．Which of the following can be best inferred from the passage?

      A．The importance of protection from radiation cannot be too overemphasized （過分強調(diào)）．

       B．The mystery about radiation remains unsolved．

       C．Cancer is mainly caused by radiation．

      D．Radiation can hurt those who do not know about its danger．