一：鞋子生命周期
一款新鞋子需要大量的广告来宣传，大量的产品进入市场后开始慢慢成熟，收到人们青睐。随着时间推移，产品开始过时，需求下降。
图片发自简书App
二：Product live cycle
主旨：The product cycle is an economic theory that was developed by Raymond Vernon in response to the failure of the Heckscher-Ohlin model to explain the observed pattern of international trade.
关键单词：economic、international trade、applies、comparative
https://en.m.wikipedia.org/wiki/Product_life-cycle_theory
