练习题
51. Unlike most of the world's volcanoes, they are not always found at the boundaries of the great drifting plates that make up the earth's surface; on the contrary, many of them lie deep in the interior of a plate.

52. The relative motion of the plates carrying these continents has been constructed in detail, but the motion of the plates with respect to another cannot readily be translated into motion with respect to the earth's interior.

53. Wearing a seat belt saves lives; it reduces your chance of death or serious injury by more than half.

54. While warnings are often appropriate and necessary--the dangers of drug interactions, for example--and many are required by state or federal regulations, it isn't clear that they actually protect the manufacturers and sellers from liability if a customer is injured.

55. At the same time, the American Law Institute--a group of judges, lawyers, and academics whose recommendations carry substantial weight--issued new guidelines for tort law stating that companies need not warn customers of obvious dangers or bombard them with a lengthy list of possible ones.

56. In the past year, however, software companies have developed tools that allow companies to "push" information directly out to consumers, transmitting marketing messages directly to targeted customers.

57. The examples of Virtual Vineyards, Amazon.com, and other pioneers show that a Web site selling the right kind of products with the right mix of interactivity, hospitality, and security will attract online customers.
58. An invisible border divides those arguing for computers in the classroom on the behalf of students' career prospects and those arguing for computers in the classroom for broader reasons of radical education reform.

59. Rather, we have a certain conception of the American citizen, a character who is incomplete if he cannot competently access how his livelihood and happiness are affected by things outside of himself.

60. Besides, this is unlikely to produce the needed number of every kind of professional in a country as large as ours and where the economy is spread over so many states and involves so many international corporations.
答案
51.跟世界上的大多数火山不同的是，它们(热点)并不总是在由构成地球表面巨大漂流板块之间的边界上出现；相反，它们中有许多位于一个板块较纵深的内部。

52.携带这些大陆板块的相对运动已经能够被详细地表述出来，但是这些板块相对于另一些板块的运动还不能轻易地解释为它们相对于地球内部的运动。

53. 系好安全带能够挽救性命，它能将丧生和重伤的概率减少一半以上。

54.尽管警告常常是适当而且必须的--比如对于药物相互作用的危险提出警告--许多警告还是按州或联邦政府规定要求给出的，然而(我们)并不清楚，如果顾客受到伤害时，这些警告是不是确实可以使得生产者和销售者豁免责任。

55.与此同时，美国法律研究所--由一群法官、律师和理论专家组成，他们的建议分量极重--发布了新的民事伤害法令指导方针，宣称公司不必提醒顾客注意显而易见的危险，也不必连篇累牍地一再提请他们注意一些可能会出现的危险。

56.但是，在过去的一年间，软件公司已经开发出工具，使得公司可以直接将信息"推出"给顾客，直接把营销讯息传递给目标顾客。

57.像Virtual Vineyards，Amazon．com这样的先驱网站表明，一个将交互性、热情服务和安全性合理结合以销售同类商品的网址是可以吸引网上客户注意的。

58.有些人为了学生的就业前景为教室里放置电脑而辩，有些人为教育的彻底改革中更为广泛的理由为教室里放置电脑而辩，这两群人之间有一条无形的界线。

59.我们更应该具有的是作为美国公民的某种观念，这个公民人物如果不能很恰当地认识到自己的生存和幸福是如何受到自身之外的事物的影响，那么其公民特征就是不完整的。

60.另外，在我们这么一个大国里，经济延展到这么多的州、涉及到这么多的国际公司，因而要按照数量培养出所需的各类专业人员是不大可能的