Space is a dangerous place, not only because of meteorsbut also because of rays from the sun and other stars.The atmosphere again acts ____1____ our protective blanket on ____2____ .Light gets through, and this is essential ____3____ plants to make the food which we ____4____ .Heat, ____5____ , makes our environments tolerable and some ultraviolet rayspenetrate the ____6____ .Cosmic(宇宙的) rays of various kinds come ____7____ the air from outer space, but ____8____ quantities of radiation from the sun are screened off. ____9____ men leave the atmosphere they are ____10____ to this radiation; ____11____ their spacesuits or the walls of their spacecraft, if they are inside, ____12____ prevent a lot of radiation damage.Radiation is the greatest known danger to explorers in ____13____ .Doses of radiation are measured in ____14____ calledrems.We all ____15____ radiation here on earth from the sun, from cosmic rays and from radioactive minerals.The____16____dose of radiation that we receive each year is about two millirems; it ____17____ according toswheresyou live, and this is a very rough estimate.Scientists have reason to think ____18____ a man can ____19____ far more radiation ____20____ without being damaged; the figure of 60 rems has been agreed.
1.A.for B.with C.on D.as
2.A.stars B.sun C.earth D.space
3.A.with B.from C.under D.for
4.A.use B.live C.eat D.get
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