Space is a dangerous place, not only because of meteors 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 penetrate the 6 .Cosmic 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 .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
答案与解析：
1.D
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.C
见上题分析。
3.D
be essential for 对 来说是首要的、基础的 ，固定搭配。
4.C
只有eat与先行词food和定语从句which we 搭配。
5.D
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.C
根据上题所讲，penetrate这个动词后面应接atmosphere 大气 这个名词。
7.D
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.B
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.A
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 。
10.B
be exposed to 暴露于 ，show 展示 ;face 面对 。
11.A
本句前半句的意思是： 人们一离开大气层就会接触射线 ;后半句意思是： 他们的太空服和太空船会阻止射线造成的损害 。前后应该是转折关系，故用but。
12.D
Do +动词原型的结构表示强调谓语动词。
13.C
由radiation和explorers可推测，应选space。本句意为射线是探险者在太空遇见的已知的最大危险。
14.B
unit 单位、单元 ;element 元素 ;part 部分 ;piece 碎片 本句意为：射线的多少可以以雷目这个测量单位测量。
15.A
receive表示客观收到;accept表示主观接受。我们受到的辐射并非主观接受。
16.D
conventional 传统的 ;common 共同的、普通的 ;general 一般的、总体的 ;normal 正常的 。本句意为：我们每年接受的正常辐射量 ，故选normal。
17.D
shift 移动 ;convert 转换 ;modify 修改 ;vary 变化 。根据句意，所处地点不同，所受辐射量也不一样 ，故选varies.
18.C
本句应填入引导宾语从句的代词，而从句不缺少主语和宾语，因而不选择what和which，又加之主句是陈述语气，故选择that。
19.A
put up with 忍受 ，固定搭配。keep up with和catch up with意为跟上,come up with意为提出。
20.B
more 后应加than。