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 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 rays(紫外线的) penetrate 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 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 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

　　第十七篇答案+解说：

　　1.【答案】D

　　【解析】act as“充当、起……作用”;act for“代表、代理”;act on“按照”。本句意为大气层起到保护伞的作用。

　　2.【答案】C

　　【解析】见上题分析。

　　3.【答案】D

　　【解析】be essential for“对……来说是首要的、基础的”，固定搭配。

　　4.【答案】C

　　【解析】只有eat与先行词food和定语从句which we…搭配。

　　5.【答案】D

　　【解析】本句意为：热不仅使我们的生产环境温度适宜，而且紫外线也能穿透大气。also一般紧跟动词;besides一般用在句前;too可用在句中，用逗号隔开。

　　6.【答案】C

　　【解析】根据上题所讲，penetrate这个动词后面应接atmosphere“大气”这个名词。

　　7.【答案】D

　　【解析】这里的come through相当于penetrate，穿透。come across“偶遇”;come to“来到”;come from“来自”。本句意为：各类来自外部空间的宇宙射线穿透大气层……，故选come through。

　　8.【答案】B

　　【解析】Valid有效的;various各种各样的;proper合适的。在四个选项中只有enormous表示“大量的”意思。

　　9.【答案】A

　　【解析】as soon as“只要”;as well as“除……之外”;as much as“和……一样多”;as possible as“尽可能的”。