Glaucon's Story of Gyges's Ring Is Used to Support Which

Glaucon's story of Gyges's ring is used to support which of the following conclusions?

A) People behave morally only because they lack the power to get away with being immoral.
B) People behave morally because they are genetically programmed to strive toward good.
C) People behave morally because acting purely out of a sense of moral duty is its own reward.
D) People behave morally because moral purity is the only way to achieve the power of Gyges's ring.