interview for parent Green Card, what need to prepair

Hello: My mom will have interview for green card soon. What kind of document I need bring with? and what kind of question they will ask? Thanks advanced 

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• Reply -863211- ♂ (450 bytes) () 04/28/2015 postreply 10:11:30

• thanks a lot -wxcreader2008- ♀ (0 bytes) () 04/29/2015 postreply 23:13:30

• sent you a message about interview questions -sagogo- ♀ (0 bytes) () 05/05/2015 postreply 09:25:10