Answer: Option B
Explanation: When the costs equal the benefits. Animals cooperate among each other when there is a mutual relationship in them.
The cost that one animal pays should be equal to the benefit that it gets from the other animal.
There are certain examples present in the nature that shows the mutual relationship among animals.
Example: Mutualism ( algae and fungi forms lichen in which the algae provides food to the fungi and fungi provides shelter to algae)