76. After people have learned that magnets attract things, centuries passed ____ they took note of the fact that magnets sometimes also repel things.

A. before B. until C. after D. since

77. He is off to Paris again tomorrow. He tells me that, with this journey, he ________ there and back twenty times.

A.will be B. will have been

C.will go D. will have gone

78. Many ways have been found_____small and simple machine to process large and complicated machine parts.

A. by using B. to use C. using D. used

79. I walked down the corridor, my footsteps_______frighteningly through the empty deserted building.

A. echoing B. echoed C. to echo D. having echoed

80. Apart from personal preferences, social context also affects—both directly and indirectly—the media and the media content to which you become exposed. For example, other members of the family often select media content that you _____, and you become exposed to it.

A. would not have selected B. should not have selected

C. must not select D. cannot have selected

76. Abefore应该理解成“(几百年过去了,人们) 才……”; 如果用after应该是…after centuries passed they took note of the fact…; 如果用until, 应该是they didn’t take note of the fact that…until centuries passed。

77. B此句意为：“他明天去巴黎,加上这次, 他就去了二十次了。”根据句意,应用将来完成时态。句中有back一词, 故D不合适。

78. Bto use…, 不定式短语做way的定语, 只是因为定语太长,故将谓语前移,使句子避免头重脚轻。by using表示方式, 做状语用; using为动名词, 不能做way 的定语, way要求不定式做定语; used, 无论从语法结构上还是从意义上都讲不通。

79. A分词短语做伴随状语, my footsteps与echo的关系是主动的,因此用现在分词。另外, 分词做伴随状语表示与谓语动词的动作同时发生, 所以用其一般式。

80. A本句意为:“除了个人喜好外, 社会环境也会直接或间接地影响你使用的媒体和媒体的内容。例如, 家庭的其他成员常常选择的媒体内容你就未必选, 可是你也得使用。”句中暗含了 “如果是你, 你就不会选” 的意思, 所以用虚拟语气合适。should not have selected表示“本不应该选”; must not select表示“一定不要选”; cannot have selected表示“一定不能选”, 过于绝对。只有would not have selected 符合句意。