八老师，我是公民，为父母申请了绿卡 (父母在国内)，拿到I-797， 大概１个月后发EMAIL 给NVC 问情况，昨天受到回复如下，我看了很糊涂，I797 就是approval for petition了吗？请您告诉我现在我需要做什么吗？万分感谢您的帮助！
Please be advised that the National Visa Center (NVC) has received your inquiry and the attached I-797 Notice of Action - Approval Notice. Unfortunately, we do not have record of receiving your approved petition from U.S. Citizenship and Immigration Services. The NVC will contact USCIS on your behalf for information on the location of this petition.