Question

a vestigial structure is
an adaptive structure present in two otherwise unrelated species.
a phenotypic trait currently preferred by the opposite sex of the same species.
a physical structure that benefits an organism in its current environment.
a structure inherited from an ancestor that no longer serves an adaptive purpose.

Explanation:

A vestigial structure is a remnant of a structure that had a function in an early ancestor. It is inherited from an ancestor but no longer serves a significant adaptive purpose in the current form of the organism. For example, the human appendix is considered a vestigial structure. It was likely more functional in our herbivorous ancestors (perhaps aiding in digestion of plant material), but in modern humans, it has lost that major digestive - related function.

• The first option describes a homologous or analogous structure (if adaptive) between unrelated species, not a vestigial structure.
• The second option describes a trait related to sexual selection (a phenotypic trait preferred by the opposite sex), not a vestigial structure.
• The third option describes an adaptive structure in the current environment, while a vestigial structure is not currently adaptive in a major way.

Answer:

a structure inherited from an ancestor that no longer serves an adaptive purpose.