Why do we have belly buttons?

Answer: Scar from umbilical cord

Scar from umbilical cord ✓ — Correct! The belly button (navel) is a scar that marks where the umbilical cord connected you to your mother in the womb. The cord provided oxygen and nutrients before birth. After birth, the cord is cut and the remaining portion dries up and falls off, leaving the belly button.

Opening for digestive system — Wrong. The belly button has no opening or connection to the digestive system. It's a closed scar on the skin surface.

Vestigial evolutionary feature — Wrong. It's not a vestigial feature—it's a necessary scar from the umbilical cord that every mammal who developed in a womb has.