Which of the following can be classified as a direct ancestor under tax definitions?

The classification of a direct ancestor under tax definitions typically refers to individuals from whom a taxpayer is descended. This includes parents, grandparents, and other forebears. A grandparent fits this definition perfectly, as they are a direct line in one's lineage, providing the relational context required to be considered a direct ancestor.

In contrast, other options do not meet the criteria for direct ancestry. A cousin is classified as a relative but is not a lineal ancestor; instead, they belong to a different branch of the family tree. A close family friend, while potentially significant in a person's life, does not have a familial relationship and thus cannot be classified as a direct ancestor. An adopted sibling, while considered family, does not ascend the family lineage and therefore does not qualify as a direct ancestor either.