Q1- 此篇文章的main purpose, 我選的是類似 introduce a new concept on the pollution-prevention method Q2- (Opportunity Cost 第一段兩字高亮) 請問Opportunity Cost 指的是為何? 我選的是to allocate resource more efficiently
有一题提到第二段的作用,我好像选择一个提到类比(analogy)的方法
opportunity cost高亮问意思我选了stop pollution before it begin; 另外的选项有possibilities loss in cost