Commensalism is a relationship where one benefits and the other is unaffected. Which option places 'Commensalism' at index 3?

• A. Mutualism
• B. Parasitism
• C. Symbiotic relationship
• D. Commensalism

Answer: (D)

Commensalism describes a relationship where one organism benefits while the other is unaffected. This exact description makes it stand apart from the others: mutualism is when both benefit, parasitism is when one benefits at the expense of the other, and a symbiotic relationship is a broad term for close living together that can include various outcomes and doesn’t specify how each organism is affected. In this list, the term that matches the given definition is the one that names commensalism. If you count from one, it sits in the fourth position; if you count from zero, it’s at index three—matching the index three phrasing.