求翻译：二十世纪六十年代，美国教育学者D.W. Johnson和R.T. Johnson兄弟等人开始着手合作性学习的研究工作，并在明尼苏达大学建立了合作学习中心，并最终十二十世纪七十年代初在美国兴起了现代的合作学习理论。早期阶段的研究(Johnson1990)着重对合作学习的内涵、要素、实施等方面的研究，把合作学习与竞争性学习、独立性学习进行比较，说明合作学习的优越性以及在教学层面的实施要点。是什么意思？

In the 1960s, American education scholars dw, johnson and rt johnson brothers and other people started the research of cooperative learning, cooperative learning center at the University of Minnesota, and eventually the early seventies, twelve tenth century the rise in the U.S. modern theory of coop

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The 20th century 60's, US educates scholar D.W. Johnson and R.T. Johnson Brother et al. start to begin the cooperative study research work, and has established the cooperation center of learning in the Univerisity of Minnesota, finally and 30 century at the beginning of 70's have started the modern%

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