填空题. A. endurable B. protection C. exposed D. if E. until F. extremely G. acts as H. decrease I. curable J. disaster K. attributed L. danger M. effective N. before O. essential 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 11 our protective blanket on earth. Light gets through, and this is 12 for plants to make the food we eat. Heat, too, makes our environment 13 Various kinds of rays come through the air from outer space, but enormous quantities of radiation from the sun are screened off. As soon as men leave the atmosphere they are 14 to this radiation but their spacesuits or the walls of their spacecraft, if they are inside, do prevent a lot of radiation damage. Radiation is the greatest known 15 to explorers in space. The unit of radiation is called "rem (雷姆)". Scientists have reason to think that a man can put up with far more radiation than 0.1 rem without being damaged. The trouble is that it is 16 difficult to be sure about radiation damage—a person may feel perfectly well, but the cells of his or her sex organs may be damaged, and this will not be discovered 17 the birth of deformed children or even grandchildren. We simply do not know yet how men are going to get on when they spend weeks and months outside the 18 of the atmosphere, working in a space laboratory. Drugs might help to 19 the damage done by radiation, but no really 20 ones have been found so far.