重点讲解：
1. feed on
以…为食；
eg. All animals including men feed on plants or other animals.
包括人类在内的所有动物都以植物或其他动物为食。
eg. Most feed entirely on plants, which makes them bothersome.
它们多数都吃植物，这使农民很讨厌它们。
2. so...that
如此……以致于；
eg. Inflation was so high that the notes were like Monopoly money.
通货膨胀严重，货币变得跟“大富翁”游戏钞票无异。
eg. The air was so still that there was hardly a ripple on the pond's surface.
没有风，池塘的水面上几乎看不到波纹。