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 radio activity 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 by killing masses of cells in vital organs. 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 a deformed 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 victim being aware at the time that damage has occurred. A person can he irradiated and feel fine, then die of cancer five, ten, or twenty years later as a result. Or a child can be born weak or liable to serious illness as a result of radiation absorbed by its grandparents.
Radiation can hurt us. We must know the truth.

The word "significant" in Paragraph 3 most probably means（）

A.And the problem is likely to grow. Over the past 30 years the proportion of children in the U. S. who are overweight has doubled, from 5% to 11% or 4.7 million kids.
B.According to a recent report in the journal Circulation, 19 of 30 children with high blood pressure developed a dangerous thickening of the heart muscle that, in adults at least, has been linked to heart failure. “No one knows if this pattern holds true for younger patients as well, ” says Dr. Stephen Daniels, a pediatric cardiologist who led the study at Children’s Hospital Medical Center in Cincinnati, Ohio. “But it’s worrisome. ”
C.Feed your children nutritious foods three times a day to keep his immune system healthy. Make sure the meals include all the food groups to ensure they are getting plenty of vitamins.
D.Fortunately the abnormal thickening can be spotted by ultrasound. And in most case, getting that blood pressure under control — through weight loss and exercise or, as a last resort, drug treatment — allows the overworked muscle to shrink to normal size.
E.If the doctor finds an abnormal result he will repeat the test over a period of months to make sure the reading isn’t a fake. He’ll also check, whether other conditions, like kidney disease, could be the source of the trouble, because hypertension is hard to be detected. The National Heart, Lung and Blood Institute recommends annual blood-pressure checks for every child over age 3.
F.High blood pressure isn’t just an issue for adults; keeping kids blood pressure levels in a healthy range is also important. In a new study reported in Hypertension, researchers found that increased exercise duration among kids leads to lower blood pressure levels, however the same cannot be said for increased intensity.
G.Meanwhile, make sure your kids spend more time on the playground than with their PlayStation. Even if they don’t shed a pound, vigorous exercise will help keep their blood vessels nice and wide, lowering their blood pressure. And of course, they’ll be more likely to eat light and, exercise if you set a good example.

A. Twitter no longer continues to be tax-free
B. Twitter’s going public has disadvantage
C. The Twitter exemption bill will reduce the San Francisco government’s revenue
D. Twitter executives are concerned about Twitter’s going public