Which Is an Example of a Mutualistic Interaction

Which is an example of a mutualistic interaction?

A) A virus infects a bird, thus reducing the bird's fecundity.
B) A blue jay chases sparrows from a bird feeder so it can eat the seeds.
C) Barnacles remain safe by riding on a whale, while the whale is unaffected.
D) A wasp lays its eggs inside a caterpillar, and the hatched wasp larvae consume the caterpillar.
E) A bacterium lives in a plant's roots and fixes nitrogen for the plant, which in turn provides nutrients to the bacterium.