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. [参考译文] 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. 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. as the dome grows, it develops seed fissures (cracks). in at least a few cases the continentmay break entirely along some of these fissures, so that the hot spot initiates the formation of a new ocean.
[参考译文] 暂缺
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.