Which interaction BEST illustrates the concept of mutualism?

AJaguars feeding on wild pigs.
BSquirrels playing with other squirrels.
CMalaria protozoans living on the blood of a host.
DNitrogen-fixing bacteria in root nodules of legumes.

Verified Answer :

DNitrogen-fixing bacteria in root nodules of legumes.

Answer:

D) Nitrogen-fixing bacteria in root nodules of legumes.

Explanation:

Mutualism is a concept in Biology that describes the ecological interaction between more than one species in which all species involved benefit from this interaction. Root nodules are generally seen on  roots of legumes and they have symbiotic relation with nitrogen-fixing bacteria, which is one form of mutualism.