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 .

Based on the preceding passage, answer the following question What may be the reason why they do n't know the grandfather 's name ?
None of the above choices .