填空题

Space is a dangerous place, not only because of meteors (流星) but also because of rays from the sun and other stars The (36) again acts as our protective blanket on earth. Light gets through, and this is (37) for plants to make the food which we eat. Heat, too, makes our environment (38) Various kinds of rays come through the air from outer space, but enormous quantities of radiation from the sun are (39) off. As soon as men leave the atmosphere they are exposed to this (40) and their spacesuits or the walls of their spacecraft, if they are inside, do (41) a lot of radiation damage.
Radiation is the greatest known danger to (42) in space. The unit of radiation is called "rem". Scientists have reason to think that a man can put up with far more radiation than 0.1 rem without being damaged; the figure of 60 rems has been agreed on. The trouble is that it is (43) difficult to be sure about radiation damage— (44) , and this will not be discovered until the birth of deformed children or even grandchildren. Missions of the Apollo flights have had to cross belts of high amounts of reins. (45) , we simply do not know yet how men are going to get on, when they spend weeks and months outside the protection of the atmosphere, working in a space laboratory. Drags might help to decrease the damage done by radiation, (46) .