Which of the following describes a relationship of mutualism?

a. a tapeworm latches itself in the intestines of a rat, feeding off all the nutrients eaten by the rat.
b. a polar bear catches a seal for dinner.
c. birds feed off the insects that are stirred up from the grasses as cattle move through.
d. oxpecker birds eat parasitic ticks off the backs of zebras

Oxpecker birds eat parasitic ticks off the backs of zebras is an example of mutualism. Mutualism is defined as a relationship between organisms in which both the individuals involved are benefitted from each other.In the case of oxpecker birds and zebras, the oxpecker birds benefit as they get their food from the parasitic ticks living on the zebra and the zebras benefit as the birds help them to get rid of the parasites.In this way, both these organisms are involved in a mutualistic relationship.