13. College students were a major force in the campaign, although participants of all ages were involved.

　　尽管参加这次运动的人涉及到各个年龄段的人，但是大学生是这场运动的主导力量。

　　14. thirty years later, the focus has changed but the urgency remains the same.

　　三十年之后，关注的焦点发生了变化，但其紧迫性依然。

　　15. X-rays were first discovered by a German scientist, Wilhelm Conrad roentgen, in 1895, almost by accident.

　　X射线最初是在1895年被一个德国科学家偶然地发现的，他的名字叫Wilhelm Conrad roentgen。

　　16. In fact, the rays could pass as easily through the fleshy part of his hand as through the black paper, but hardly at all through the bone.

　　事实上，就像穿过一张黑纸一样，射线很容易穿过手部的肌肉，但却根本不能穿过骨骼.

　　17. The answer would seem to lie in nuclear power stations.

　　看来问题在于核电站。

　　18. If the world population goes on increasing at its present rate, we may, in fifty years’ time, be burning up so much energy that we would damage the earth’s atmosphere.

　　如果世界人口继续以当前这种速度增长的话，也许，五十年后，这样燃烧如此多的能源将会致使我们破坏地球的大气层。

　　19. Psychologists deal with the minds and behavior of people.

　　心理学家研究人们的心理与行为。

　　20. Several people have been instrumental in the field of psychology.

　　一些人在心理学领域起了很大作用。

　　21. It is only when we cannot see perfectly that we realize how important our eyes are.

　　只有当我们看东西不清楚时，我们才意识到我们的眼晴是多么地重要。

　　22. They can see things that are far away, but they have difficulty in reading a book unless they hold it at arm’s length.

　　这些远视的人们能看清远处的东西，但是他们读书却很困难，除非他们把书举到一臂远的距离处去看。

　　23. The same comment is made from generation to generation and it is always true.

　　同样的理论代代相传，而且总是正确。

　　24. Events that the older generation remembers vividly are nothing more than past history.

　　老一代记忆犹新的重大历史事件对年轻人来说不过是过眼烟云而已。