They were really nice and the grandma was so sweet . The grandpa asked when Oma left Germany , and I said around ' 55 and he nodded and said , " She was right , she was right , " So that was funny . The grandmother 's name is Johanna , but I do n't know the grandfather 's name .

Question: What may be the reason why they do n't know the grandfather 's name ?
Answer: None of the above choices .They were n't supposed to know it .They are undercover .They are in the witness protection program .