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听下面一段材料,回答第18至第20题 Mr White is my friend Jenny' s father. He works as a science teacher in England. Although he has a o car, he usually walks to work. In his free time, he likes to invent different kinds of things. He has made 40 inventions. His first invention was made in 1989 It was machine that was used to cut grass. ThenL 1991, he made his second invention. It was used to k, wash clothes. His most important invention was a, machine that was used to plant rice. It was finally finished in 2012. He spent three years on it. Now y several factories are producing this kind of machine. They are popular with farmers