[单项选择]

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
A. discovery
B. invention
C. search
D. research

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