Passage Three

　　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 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(畸形的)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 a space laboratory.Drugs might help to decrease the damage done by radiation，but no really effective ones have been found so far.

　　44.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 heat necessary for human survival

　　D.it screens off the falling meteors

　　A 推断判断题。由第一段可知，流星和来自太阳及其他星体的射线，使得宇宙空间成为危险之地，而大气层可以充当地球的保护毯。由此可知，大气层在保护人类不受有害射线的辐射方面至关重要，故选A。

　　45.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

　　B 推理判断题。由第二段第四句可知，辐射对人体的危害一时难以显现，它可能会在其子女或孙子女的身上体现出来。B项符合题意，故选B。

　　46.It can be inferred from the passage that .

　　A.the Apollo mission was very successful

　　B.protection from space radiation is no easy job

　　C.astronauts will have deformed children or grandchildren

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

　　B 推理判断题。由最后一句“Drugs might…but no really effective ones have been found so far.”可知，目前人类还没有找到有效的方法去避免辐射的危害，所以免受辐射危害并非易事，故选B。

　　47.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

　　C 主旨大意题。通读全文可知，文章开头提到，宇宙空间里存在很多辐射，第二段又紧紧围绕辐射对人类的影响展开论述。C项符合题意，故选C。

　　Passage Four

　　How men first learned to invent words is unknown;in other words, the origin of language is a mystery.All we really know is that men, unlike animals, somehow invented certain sounds to express thoughts and feelings, actions and things, so that they could communicate with each other;and that later they agreed upon certain signs, called letters, which could be combined to represent those sounds and which could be written down.Those sounds, whether spoken, or written in letters, we call words.

　　The power of words, then, lies in their associations—the things they bring up before our minds.Words become filled with meaning for us by experience;and the longer we live, the more certain words recall to us the glad and sad events of our past;and the more we read and learn, the more the number of words that mean something to us increases.

　　Great writers are those who not only have great thoughts but also express these thoughts in words which appeal powerfully to our minds and emotions.This charming and telling use of words is what we call literary(文字的)style.Above all,the real poet is a master of words.He can convey his meaning in words which sing like music,and which by their position and association can move men to tears.We should therefore learn to choose our words carefully and use them accurately,or they will make our speech silly and rude.

　　48.The origin of language .

　　A.is a legend handed down from the past

　　B.is reflected in sounds and letters

　　C.dates back to the prehistoric period

　　D.is a problem not yet solved

　　D 事实细节题。文章第一段第一句指出,我们还不知道人们第一次是怎样创造单词的，换句话说，语言的来源仍是个谜(the origin of language is a mystery),还没有得到解决。故选D。

　　49.One of the reasons why men invented certain sounds to express thoughts and actions is that .

　　A.they could agree upon certain signs

　　B.they could write them down

　　C.they could communicate with each other

　　D.they could combine them

　　C 事实细节题。文章第一段第二句指出，人们创造某些声音来表达自己的思想感情、行动和事物，目的是他们可以互相交流。故选C。

　　50.What is true about words?

　　A.They are used to express feelings only.

　　B.They can not be written down.

　　C.They are represented either by sounds or letters.

　　D.They are visual letters.

　　C 事实细节题。文章第一段讲到，人类起初用某种声音进行交流，后来又有了字母，字母结合起来可以代表声音，也可以写下来。因此这些说出来的声音也好，用字母写出来的声音也好，都被我们称为words。故选C。

　　51.The real power of words exists in their .

　　A.accuracy

　　B.beauty

　　C.charm

　　D.representative function

　　D 推理判断题。由文章第二段第一句“The power of words,then,lies in their associations—the things they bring up before our minds.”可知,words的魅力在于它的代表性功能(representative function)。