你没看exempt individual 的时间限制, F1是5年历年

, 第六年起就可以算RA了.

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When a Student is Not Exempt

You will not be an exempt individual as a student if you have been exempt as a teacher, trainee, or student for any part of more than 5 calendar years, unless you establish to the satisfaction of the IRS that you do not intend to reside permanently in the United States, and you have substantially complied with the requirements of your nonimmigrant status. The facts and circumstances to be considered in determining if you have demonstrated an intent to reside permanently in the United States include, but are not limited to:


http://www.irs.gov/businesses/small/international/article/0,,id=96344,00.html