Which statement is an example of commensalism

Option A

Explanation:

In a commensalism relationship, two species live in association with each other where one species gets the benefit of this relationship while the other is neither harmed nor benefited.  

Here in option A, Egrets eat the insects left after livestock graze but this act of Egrets has no impact (positive or negative) on the the livestock. Thus, it is an example of commensalism