挖掘矿石，提炼生铁，铸造纯钢
Human knowledge is not (or does not follow) a straight line, but a curve, which endlessly approximates a series of circles, a spiral. Any fragment, segment, section of this curve can be transformed (transformed one-sidedly) into an independent, complete, straight line, which then (if one does not see the wood for the trees) leads into the quagmire, into clerical obscurantism (where it is anchored by the class interests of the ruling classes). ---Lenin
人类的知识不是（或不遵循）一条直线，而是一条曲线，它不断地接近一系列圆，螺旋。这条曲线的任何片段，分部，节可以转化（转化片面）成为一个独立的，完整的，直线的，然后（如果见木不见林）带领入泥潭，到蒙昧主义（它是由统治阶级的阶级利益）固定。
