综合写作
reading passage：bison 数量减少 三点原因：1.bison is a source of food 2.cattle and horses compete 3.guns
lecture：1.如果是由于bison作为食物，数量应该是从east开始减少 事实上是west开始减少
2.天气寒冷，bison有厚厚的毛，可以抵抗寒冷，而cattle and horses就不能与之竞争
3.nation used guns for hundreds of years.
写作：Rather than help their children do school work，parents should encourage their children do work independently. Do you agree or disagree?
