A、Any astronaut returning from the universe is safe. B、Any astronaut returning from the universe suffers a lot. C、We can assume

Not long ago it was assumed that the dangers man would meet in space would be terrible, the main ones being radiation and the danger of being hit by meteors. It is perhaps worth remembering that less than two centuries ago the dangers of train travel seemed similarly terrible. A man would certainly die, it was thought, if carried along at a speed of thirty kilometres per hour.
    There are two sorts of radiation man must fear in space. The first is radiation from the sun, and this is particularly dangerous when the sun is very active and explosions are occurring on its surface. The second less harmful form comes from the so-called Van Allen Belts. There are two areas of radiation about 1,500 miles away from the earth. Neither of these forms of radiation are danger to us on the earth, since we are protected by our atmosphere. Specifically, it is that part of our atmosphere known as the ozonosphere which protects us. This is a belt of the chemical ozone between 12 and 21 miles from the ground, which absorbs all the radiation.
    Once outside the atmosphere, however, man is no longer protected, and radiation can be armful in a number of ways. A distinction must be drawn between the short and long-term effects of radiation. The former are merely unpleasant, but just because an astronaut returning from a journey in space does not seem to have been greatly harmed, we cannot assume that he is safe. The long-term effects can be extremely serious, even leading to death.
Questions 23 to 25 are based on the passage you have just heard.
23. What forms of radiation are feared by astronauts?
24. What can we infer from the passage?
25. Why can’ t people on earth be harmed by radiation?