Realists Argue That States' Concern with Relative Gains Will Undermine

Realists argue that states' concern with relative gains will undermine international cooperation.What do they mean by this?

A) States will not cooperate since they have relatively little to gain from doing so.
B) States cannot be sure they will gain anything from cooperation,so they have little incentive to try.
C) States are reluctant to cooperate because they fear their partners will cheat,and no one will gain from cooperation.
D) States will be reluctant to cooperate even for mutual gain because their partners may benefit more,gaining additional power to use against them in the future.