第三部分：阅读理解（共20小题；每小题2分，满分40分）
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Last week，Bill Gates retired from full-tine．rime work at the world’s biggest computer software company, Microsoft．He will remain chairman of the company he established with Paul Allen in nineteen seventy-five．
Mister Gates leaves Microsoft at a time of change in the computing industry．Microsoft grew at a time when personal computers，or PCs，were replacing big mainframe computers as the main computing tools．He showed that huge profits could be made in software as PCs increasingly were found “on every desk and in every home．”
Early on，Microsoft understood the importance of the “network effect．” That is．software is the kind of product that increases in value as more people buy and use it．
