Space is a dangerous place, not only because of meteors(流星)but also because of rays from the sun and other stars.Theatmosphere again acts 1 _our protective blanket on 2_ .Lightgets through, and this is essential 3_ plants to make the foodwhich we 4_ .Heat, 5_ , makes our environments tolerable andsome ultraviolet rays(紫外线的) penetrate the 6_ .Cosmic(宇宙的) rays of various kinds come 7_ the air from outer space, but8_ quantities of radiation from the sun are screened off. 9 _menleave the atmosphere they are 10_ to this radiation; 11_ their spacesuits or the walls of theirspacecraft, if they are inside, 12_ prevent a lot of radiation damage.Radiation is the greatest knowndanger to explorers in 13 _.Doses of radiation are measured in 14 _called“rems (雷目)”.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 toswheresyoulive, and this is a very rough estimate.Scientists have reason to think 18_ a man can 19_ far moreradiation 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
 

　　5.A.again B.also C.besides D.too
 

　　6.A.environment B.space C.atmosphere D.earth
 

　　7.A.across B.to C.from D.through
 

　　8.A.valid B.enormous C.various D.proper
 

　　9.A.As soon as B.As well as C.As much as D.As possible as

　   10.A.shown B.exposed C.faced D.covered
 

　　11.A.but B.because C.so D.so that
 

　　12.A.get B.make C.have D.do
 

　　13.A.earth B.atmosphere C.space D.environment
 

　　14.A.pieces B.units C.parts D.elements
 

　　15.A.receive B.accept C.bring D.catch
 

　　16.A.conventional B.commonC.general D.normal
 

　　17.A.shifts B.converts C.modifies D.varies
 

　　18.A.what B.which C.that D.why
 

　　19.A.put up with B.keep up with C.come up with D.catch up with
 

　　20.A.from B.than C.as D.away












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