填空题 Nuclear radiation cannot be detected by human senses. 1 However, 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 or sense them without a radio receiver. 2 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 by killing a great number of cells in very important organs. 3 There is no level of radiation that is completely safe. If the radiation does not hit anything important, the damage may not be great. This is the case when only a few cells are hit. 4 But if the few cells are only damaged, and if they reproduce themselves, you may be in trouble. They reproduce themselves in a deformed way. 5 Sometimes this does not turn up for many years.
A. They can grow into cancer.
B. But even the lowest levels can do serious damage.
C. Similarly, we can"t sense radio activity without a radiation detector.
D. The cells in a very low level has no effect on people or animals.
E. Your body will replace the dead cells with healthy ones.
F. People have studied nuclear radiation for a quite long time.
G. It can"t be seen or heard, or touched or tasted.