四级练习2015.05.28
[audio]http://sound.yywz123.com/tingbbs/cet4/cet420150528.mp3[/audio]But even the lowest levels can do serious damage. There is no level of radiation that is completely safe. (1)___________________________________
This is the case when only a few cells are hit, and if they are killed immediately. Your body will replace the dead cells with healthy ones. (2)___________________________________ 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 appear 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. (3)_____________________________________________then die of cancer ten or twenty years later as a result. Or a child can be born weak or easy to be seriously ill as a result of radiation absorbed by its grandparents.
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