Hi, I'm trying to get my parents green card. Everything went smooth until the cases got NVC (National Visa Center). My father's case was approved three month later and he's already gone through interveiw and got his visa a couple weeks ago. Unfornationaly, my mother's case is still pending at NVC. I don't know why? Anyone had experience like this? I called NVC many times and they told nothing but it's under review. What needs to be review? How long it could take?