They are expensive to produce but cheap toreproduce and distribute, and therefore exhibit strong economies of scale with incentives to an over-supply.
它们的生产成本高昂，但再生产和销售的成本低廉，因而展现出强大的规模经济效益，并容易诱发供应过量。
2
Physical scale models for the Yellow River (YR) can be used toreproduce, simulate and test the phenomenon that happened on the real YR, so they can facilitate exposure of the natural laws concerned.