17．Nuclear power's danger to health，safety，and even life itself can be summed up in one word：radiation．
Nuclear radiation has a certain mystery about it，partly because it cannot be detected 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 immediately by killing masses of cells in vital organs．But even the lowest levels can do serious damage．There is no levels of radiation that is completely safe．If the radiation does not hit anything important，the damage may not be serious．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．But if the few cells are only damaged，and if they reproduce themselves，you may be in trouble．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 victim being aware at the time that damage has occurred．A person can be irradiated（辐射）and feel fine，then die for cancer five，ten，or twenty years later as a result．Or a child can be born weak as a result of radiation absorbed by its grandparents．
Radiation can hurt us．We must know the truth．
61．What is the main idea of the passage？C
A．How to detect nuclear radiation．
B．How radiation kill a man．
C．The mystery about nuclear radiation．
D．Serious damage caused by nuclear radiation．
62．Which of the following statements is true？A
A．Nuclear radiation can cause cancer to human beings．
B．Nuclear radiation can be safe to human beings if its level is low．
C．Nuclear radiation can be detected by human senses．
D．Nuclear radiation is just like common radio waves．
63．How can nuclear radiation kill an animal？C
A．By damaging its heart．B．By killing a few cells．
C．By killing many cells in important organs．D．By hitting any place in its body．
64．What is not the reason why nuclear radiation has a certain mystery？C
A．The hurt cells can stay in the body many years and then grow into cancer．
B．It can do harm to a person while the victim isn't aware the damage has occurred．
C．Nuclear radiation can kill a person very easily．
D．Radiation can seldom kill a person immediately．
65．If a human being is hit by nuclear radiation，he mayD．
A．die of cancer after many years B．die immediately
C．have a child who may be born weak D．all of the above．
