Hi,
That is a very touchy question. I am aware that you have a need for a green card so you will not have to go back to the country where you come from. You are thinking of marriage of convenience. I strongly discourage you from doing this. The reasons are:
1. If INS will learn that you married this person because you need a green card, you will be deported.
2. You will feel really bad if you married someone who is a U.S. citizen but will possibly abuse you physically, mentally or sexually.
It is better for you to find a man who is a U.S. citizen by the conventional way like meeting and falling in love with one of your classmates and who possibly will have lots in common with you.
Don't marry just anybody in a hurry because you may have lots of problems later. Marry because you love the person and because you are proud to have him as a husband. Good luck.