知识点：
1.essey的结构
2.while
Smartphone, while usefue, present serious problem. In this essay, I'll talk about the harmful effects of
while usefue=even though smartphone is useful，the present serious problem...
3.如何引用
According to a survey by the American Psychological Association，“People .......”(Bubb 2017)
4.结尾
写作中一般用：In sum,In summary
To sum up(more in meeting)
5.style guide:
Chicago Manual of style( for booke,novels,)
The Associated Press style guide(newspaper)
MLA style guide(the Modern Language Association style guide)(for humanities)
