The correct answer is C. Birds following grazing animals who stir up insects
Step-by-step explanation:
In commensalism, one organism benefit from others without causing a positive or negative effect on this organism as it occurs in mutualism or parasitism. This type of biological interaction is usually a long-term interaction and benefits one of the organisms through shelter, food, protection, among others. This can be seen in the case of "Birds following grazing animals who stir up insects" because the actions of grazing animals provide birds with food which represents a benefit for birds; additionally grazing animals are neither harm nor benefit from this.