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 as our protective blanket on earth. Light gets through, and this is essential for plants to make the food which we eat. Heat, too, makes our environment endurable. Various kinds of rays come through the air from outer space, but enormous quantities of radiation from the sun are screened off. As soon as men leave the atmosphere they are exposed to this radiation but their spacesuits or the walls of their spacecraft, if they are inside, do prevent a lot of radiation damage.

Radiation is the greatest known danger to explorers in space. The unit of radiation is called "rem". Scientists have reason to think that a man can put up with far more radiation than 0.1 rem without being damaged; the figure of 60 rems has been agreed on. The trouble is that it is extremely difficult to be sure about radiation damage — a person may feel perfectly well, but the cells of his or her sex organs may be damaged, and this will not be discovered until the birth of deformed children or even grandchildren. Missions of the Apollo flights have had to cross belts of high radiation and, during the outward and return journeys, the Apollo crew accumulated a large amount of rems. So far, no dangerous amounts of radiation have been reported, but the Apollo missions have been quite short. We simply do not know yet how men are going to get on when they spend weeks and months outside the protection of the atmosphere, working in space laboratory. Drugs might help to decrease the damage done by radiation, but no really effective ones have been found so far.

1. According to the first paragraph, the atmosphere is essential to man in that           .

A. it protects him against the harmful rays from space

B. it provides sufficient light for plant growth

C. it supplies the hear necessary for human survival

D. it screens off the falling meteors

2. We know from the passage that              .

A. exposure to even tiny amounts of radiation is fatal

B. the effect of exposure to radiation is slow in coming

C. radiation is avoidable in space exploration

D. astronauts in spacesuits needn’t worry about radiation damage

3. The harm that radiation has done to the Apollo crew members            .

   A) is insignificant                    B) seems overestimated

   C) is enormous                      D) remains unknown

4. It can be inferred from the passage that            .

A. the Apollo mission was very successful

B. protection from space radiation and cure the related disease are no easy job

C. astronauts will certainly have deformed children or grandchildren

D. radiation is not a threat to well-protected space explorers

5. The best title for this passage would be             .

A. The Atmosphere and Our Environment

B. Research on Radiation

C. Effects of Space Radiation

D. Importance of Protection Against Radiation

参考答案 20. A B D B C

太空是个危险的地方，（其危险）不仅仅来自流星，而且也来自太阳和其他恒星发出的射线。大气层再次起到地球保护毯的作用。光穿过大气层，提供了我们食用的食物所必须的光照；热透过大气层，使我们生活的环境可以忍受。各种各样源自外太空的射线穿过大气层，但是来自太阳的大量辐射被（大气层）屏蔽。一旦人类离开大气层，他们就会被暴露在辐射中，但是宇航服或者飞船的确可以防止辐射造成的伤害。
辐射是人类已知的最大的太空威胁。辐射的单位叫做“雷姆”。科学家有理由相信人类可以忍受远远大于0.1雷姆的辐射而不会受到伤害，对此科学家的共识是60雷姆。问题是确认辐射（对人类）造成的伤害是及其困难的 – 人们可能会感觉非常良好，但是其生殖器官的细胞可能已经遭到了伤害，而这只有到畸形后代才可以被发现。阿波罗号飞行员们必须穿越高辐射带，并且在仓外执行任务和返回期间阿波罗飞行员（体内）累积了大量的辐射。迄今为止没有任何危险辐射量的报告，但是，阿波罗飞行时间很短。我们尚不了解如果人类在没有大气层保护的情况下在太空实验室工作几个星期或者几个月，情况会怎样发展。药物也许有助于减少辐射的伤害，但是到目前为止我们尚未找到真正有效的药物。