What do you call your father's mother?

Your father’s mother is your paternal grandmother, if you want to get specific with it. The answer is B. If you were talking about your father’s father, you’d want answer A, your grandfather.

Your mother is the person who gave birth to you, so unless there’s some weird dynamic in this family, you wouldn’t use mother for your father’s mother. An aunt is the sister of one of your parents - either father or mother - so that is also wrong.

Most seventh graders will know this already. I say most because there are some that grow up without knowing grandparents because they passed away when they were younger or before they were born. That’s just how the world works, and it can be rather unfortunate.