Hey Hazem, how are you, my friend? I hope you are doing just fine! ''Thousands of personnel files were carefully checked. The search proved beyond any question that no significant difference existed in native intelli­gence. What's more, differences in education did not explain the difference in selling success. The differ­ence in the very successful and the very unsuccessful finally reduced to differences in attitudes or differ­ence in thought-management''. 1) ''beyond any question'' = in this case, the word ''beyond'' is used to mean ''surpassing'' or even ''exceeding''. So, you may get this idea: ''...beyond any question...'' = ...exceeding/surpassing any question... = ...undoubtedly/without a doubt/certainly... 2) ''reduced to'' = the idiom ''reduce to'' might mean ''decrease/bring something to a(nother)level''. So, the idea conveyed is that the differences in the very successful and the very unsuccessful finally ''changed to'' or ''turned out to be'' those in attitudes or thought-management. Did you get the idea? Hope that helps!!!

"Reduce" in this sense means to remove extraneous elements or view the problem in its most basic terms. As an analogy, think about reducing a fraction (turning 8/12 into 3/4).

thanks natalia but i didnt find this meaning in the dictionary about the word( redue to)what i found was turn into or change...but ur answer as turn out to be does make sense

beyond any question=beyond any doubt, certainly reduced to= turned out to be (just difference in attitudes, not difference in education or intelligence)