题目

It has been more than twenty years since pioneering British computer programmer, Sir Tim Berners Lee, created the World Wide Web. But could he have ever imagined how much the web would change our lives? And would he approve of how some British students are taking advantage of his invention? Universities and exam boards around the UK are becoming increasingly concerned with the rising number of cases of plagiarism, many of which are facilitated (助长) by the Internet access. In the UK most school and university students complete coursework throughout the academic year which contributes toward下列物质中，属于混合物的是 （用序号填空，下同），属于纯净物的是 ．①生锈的铁钉        ②冰水       ③生理盐水         ④臭氧．