With Respect to the Public Goods Game, a "Hump-Shaped" Contribution

With respect to the public goods game, a "hump-shaped" contribution profile refers to the fact that:

A) For some people, contributions increase in the expected contribution of other group members but only up to point; thereafter, contributions decrease with an increase in the expected contribution of other group members.
B) Some people always contribute their entire token endowment to the public account regardless of what others do since this is the strategy commensurate with obtaining the social optimum.
C) Some people's contributions are positively correlated with their prior beliefs about the expected contribution of other group members.
D) Some people always free-ride no matter what the expected contribution of other group members, since free-riding is commensurate with the Nash equilibrium of this game.