primary supporting sentences是什么意思?

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.