Space is a dangerous place, not only because of meteors(流星) but also because of rays from the sun and other stars. The atmosphere again acts 1our protective blanket on earth. Light gets through, and this is essential for plants to make the food which we 2. Heat, too, makes our environments tolerable and some ultraviolet rays(紫外线的) penetrate the 3. Cosmic(宇宙的) rays of various kinds come 4the air from outer space, but enormous quantities of radiation from the sun are screened off. As soon as men leave the atmosphere they are exposed to this radiation; 5their spacesuits or the walls of their spacecraft, if they are inside, 6prevent a lot of radiation damage. Radiation is the greatest known danger to explorers in 7. Doses of radiation are measured in units called “reins (雷目)”. We all 8 radiation here on earth from the sun, from cosmic rays and from radioactive minerals. The “normal” dose of radiation that we-receive each year is about two milligrams; it 9according to where you live, and this is a very rough estimate. Scientists have reason to think that a man can put up with far more radiation 10without being damaged; the figure of 60reins has been agreed.A. withB. asC. atmosphereD. spaceE. shiftF. eatG. earthH. thanI. butJ. variesK. recieveL. doM. convertsN. useO. through