its urgent pls reply

[nsk]

kinldy answer me ,as i applied for status change ,and i got a received letter from USCIS that my application is in process,today i got another letter to provide additonal evidence to support my application,kindly let me know that my entry will expire on dec 6,2010 .If i willnot get the response from USCIS and it will take longer time to process my application then can i stay in USA,till I get decision or its better for me not to wait and leave united states before 6 dec,even my application for status change in process.
some one told me that i will get the answer from USCIS or not but i have to leave US before my entry expires ,other wise it make a difficulties for me in future .
I need your suggestion.
Thanks

[immihelp]

As long as your application is pending at USCIS, you are in legal status.