【案例分析题】

Here is the story of rubber.From the earliest time it was common knowledge to the Peruvians（秘鲁人）that when a cut was made in the outside skin of a rubber tree，a white liquid like milk came out，and that from 【21】______a sticky mass of rubber might be made.This rubber is 【22】______when warm，so that it is possible to give it any 【23】______.The Peruvians made the 【24】______that it was very good for keeping out the wet.Then in the early 1800’s，the Americans made use of it for the first time.First they made overshoes to 【25】______their feet dry.Then came a certain Mr.Mackintosh，who made coats of cloth covered with natural rubber.From that day to this we have been coating cloth with rubber as Mr.Mackintosh 【26】______，and our raincoats are still named after 【27】______.
These first rubber overshoes and raincoats were all soft and sticky 【28】______summer，and hard and inelastic （没有弹性的）in the winter 【29】______it was cold.【30】______the rubber we have today is soft and elastic，it is very strong 【31】______in the warmer summer and the colder winter.This was made possible by a man 【32】______Goodyear.After many 【33】______，he found that nitric acid（NHO3）made the rubber 【34】______better，but it is not hard and strong enough.Then strange thing 【35】______.A friend of his，Nicholas Hayward，had the 【36】______in his sleep that rubber might be made hard and strong if mixed 【37】______sulphur and put in the sun.Goodyear put this idea to the test，and saw that it did have more or less the desired 【38】______though somewhat less than more.The only effect it had was on the outside of the rubber.【39】______is common knowledge now that the way to make rubber hard and strong is by heating it with sulphur.It took Goodyear four more years to find this heating method.When 【40】______he did it，he had nothing at all.Everything of the smallest value had been used to get money，even his sons’school-books.

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