单项选择题

阅读下列短文，从每题所给的四个选项([A]、[B]、[C]和[D])中选出最佳选项。
A

Reading is not the only way to gain knowledge of the work in the past. There is another large reservoir (知识库) which may be called experience, and the college student will find that every craftsman (工匠) has something he can teach and will generally teach gladly to any college student who does not look down upon them. But the demonstration (示范) and report of what happens, and how it happens are correct even if the reports are in completely unscientific terms (术语). Presently the college student 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, of old country customs, of folklore (风俗). All 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.

The main idea of this passage is about