Why Can It Be Said That Extended Family Is Important

Why can it be said that extended family is important for family life for both practical and psychological reasons?

A) A reproductive couple and its children exist as a unit outside of siblings, cousins, aunts, uncles, and grandparents.
B) Individual identity is rooted in biologically based descent and cooperative kinship networks within larger social groups.
C) An extended family helps children achieve the provision of unconditional altruistic care despite status ascribed by birth.
D) Human beings exist within a family's cultural envelope that is dictated by evolutionary biology and societal norms.