参考范范文： I was given an opportunity to study in the US one summer. This opportunity is very important to me for several reasons. Firstly, it was the first time I went abroad. I had imagined going abroad ever since I was a little kid. I never got a chance until that day I received a call from an administrator in my college telling me that I was granted the opportunity to study abroad for the summer vacation. Secondly, I learned and experienced a lot from this opportunity. In this exchange program, I was assigned a partner who was also a college student in the US. He introduced me to his family, took me out to valley faire and instructed me how to use Linux in the computer lab.
2、有必要的连接词（but, moreover 之类）；
4、看情况适当使用从句长句（which, who 什么的就算）；