英语四级考试完形填空寒假练习（17）

　　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

　　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