| Today much rubber is synthetic. It
would seem that there would be less opportunity for accidents in creating this
artificial product. Nevertheless the first synthetic rubber was produced by
accident, an even stranger accident than that which happened to Charles
Goodyear. In 1917, Professor Harry L. Fisher, a teacher of organic chemistry at Columbia University, was asked by the United States War Department to prepare chemical compounds, The War Department planned to test these compounds in order to decide how effective they would be against an enemy. Fisher was given a list of 20 such compounds, and number 13 on the list was a chemical made with sulfur. Some people think that is an unlucky number, and Fisher thought it was when he first heated the chemicals in his laboratory The result was a bad - smelling, sticky substance that certainly had A. the first synthetic rubber was produced by Charles Goodyear B. if it had not been for a traffic accident, we would not have had synthetic rubber C. more need for rubber helped the development of synthetic rubber D. the first synthetic rubber came into being totally unexpectedly [单项选择]
Modern computers are electronic and （） devices. The basic building block of a modem computer is a （） Modern computers are electronic and （） devices.A. chemical B. digital C. phisical D. anal0g [单项选择]Every means ______ but without much result.
A. have been tried B. has been tried C. have tried D. has tried [单项选择]Every means ______ been tried but without much result.
A. has B. have C. had D. is [单项选择]
Woman: People today are very much worried about unemployment in the world, both in developed countries and in developing countries. 我来回答: 提交
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