[单项选择]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 (67) our protective blanket on earth. Light gets through, and this is (68) for plants to make the food (69) we eat. Heat, too, makes our environment endurable. Various kinds of rays (70) through the air from outer space, (71) enormous quantities of radiation from the sun are (72) off. As soon as men leave the atmosphere they are (73) to this radiation but their spacesuits or the walls of their spacecraft, (74) they are inside, do prevent a lot of radiation damage.
Radiation is the greatest known (75) to explorers in space. The unit of radiation is called "rein (雷姆)". Scientists (76) reason to think that a man can put up with far more radiation (77) 0.1 rem without being damaged; the figure of 60 rems has been agreed on. The trouble is that it i

[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 atmosphere again acts 【B1】 our protective blanket on 【B2】. Light gets through, and this is essential 【B3】 plants to make the food which we 【B4】. Heat, 【B5】, makes our environments tolerable and some ultraviolet rays (紫外线的) penetrate the 【B6】. Cosmic(宇宙的) rays of various kinds come 【B7】 the air from outer space, but 【B8】 quantities of radiation from the sun are screened off. 【B9】 men leave the atmosphere they are 【B10】 to this radiation; 【B11】 their spacesuits or the walls of their spacecraft, if they are inside, 【B12】 prevent a lot of radiation damage. Radiation is the greatest known danger to explorers in 【B13】. Doses of radiation are measured in 【B14】 called "rems(雷目)". We all 【B15】 radiation here on earth from the sun, from cosmic rays and from radioactive minerals. The "【B16】" dose of radiation that we receive each year is about two millirems; it 【B17】 accordi
A. A．shown
B．exposed
C．faced
D．covered