I am US Citizen. I applied for Parent's Green Card as soon as they arrived in USA on Visitor Visa. I applied within 1 week of their arrival in USA on visitor Visa.
I applied all application forms: I-130, I-864, I-485 and Medical Examination Report.
I had submitted all the required supporting documents to prove parent-child relation ship and their marriage certificate.

Their fingerprinting was done 2 weeks ago.

Now we have received an Interview for I-485 for my parents.

My questions:
1.> Why did they send us Interview Notice?
2.> What questions are they going to ask us in Interview?
3.> What results may come from Interview?
4.> Is there any possibilities of denial of I-485 in interview?

NOTE:
My friend also applied for his mother but she received her Green card by mail without any interview. Her application was also applied as soon as she came on Visitor visa.

Appreciate your answer / experience.

Thanks.