单项选择题

Reading is not the only way to gain knowledge of all the work in the past. There is another way which may be called experience. College students will find that every craftsman (工匠) has something to teach and will generally teach gladly if they don’t look down on him. The information from the craftsman differs from that in textbooks and papers because that its theoretical part -- the explanations of why things happen -- is frequently quite strange. But the demonstration (示范) of what happens, and how it happens are correct even if they are in completely unscientific words. Presently the college students will learn, in this case also, what to accept and what to reject.
Another source of knowledge is the vast store of traditional practices handed down from father to son, or mother to daughter in old country customs. M1 this is very difficult for a college student to examine, for much knowledge and personal experience is needed here to separate good plants from wild grass. 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 existed in this area long ago.

In the last paragraph, the phrase "this wide, confused wilderness" refers to ().

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