单项选择题

Questions 46 to 50 are based on the following passage: Reading is not the only way to acquire knowledge of preceding work. There is another large reservoir which may be called experience, and the college student will find that every craftsman has something he can teach and will teach gladly to any college student who does not look down upon them. The information from these quarters differs from that in textbooks and papers chiefly in that its theoretical part －the explanations of why things happen — is frequently quite fantastic. But the demonstration and report of what happens, and how it happens, are sound even if the reports are in completely unscientific terms. Presently the college student will learn, in this case also, what to accept and what to reject. One important thing for a college student to remember is that if Aristotle could talk to the fisherman, so can he. Another source of knowledge is the vast store of traditional practices handed down from father to son, or mother to daughter, of old country customs, of folklore. All this is very difficult for a college student to explore, for much knowledge and personal experience is needed here to separate good plants from wild weeds. The college student should learn to realize and remember how much of real value science has found in this wide, confused wilderness and how often scientific discoveries turned out to be rediscoveries of what had existed in this wilderness long ago.

The main idea of this passage is about （）.

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