primary supporting sentences
主要支撑句。是指在一篇文章中，主题句之后，用以解释你的主题句，阐述并支撑你的观点的主要句子。
例如在下面这段文章中：
There are three reasons why I want to learn English.
One reason is that English has become an international language.
It is now used by most international companies, including the company where I work, for business communication.
Another reason why I want to learn English is so that I can travel to English-speaking countries.
The United States, England, Australia and many other countries all use English as their primary language.
Finally, I want to learn English because I plan to move to the U.S. in the future.
I will become a manager for my company soon. For those reasons, I want to learn English.
There are three reasons why I want to learn English.即为主题句。而其后的，One reason is....,another reason ...（也就是我分出的每段的第一句话）便是primary supporting sentences了。
在阅读理解时，抓住主题句和主要支撑句是理解文章意思和答题的关键；而在写作中，则要注意自己支撑句的措词和语法，因为这是老师评分的重点检查部分。
