GOOGLE dude...
here is part-answer to your first question: http://www.law.georgetown.edu/intl/F1.html
here is another one from http://www.travel.state.gov/visa/temp/types/types_1268.html#entry
...As an example regarding duration of status, if you have a visa that is valid for five years that will expire on January 1, 2001, and you are admitted into the U.S. for the duration of your studies (often abbreviated in your passport or on your I-94 card as "D/S"), you may stay in the U.S. as long as you are a full time student. Even if January 1, 2001 passes and your visa expires while in America, you will still be in legal student status. However, if you depart the U.S. with an expired visa, you will need to obtain a new one before being able to return to America and resume your studies. A student visa cannot be renewed or re-issued in the United States; it must be done at an Embassy or Consulate abroad....
Use these information at your own risk. Go google for the rest of the information, lasy assss..
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