One of the Weaknesses of Cultural Relativism as an Explanation

One of the weaknesses of cultural relativism as an explanation of morality is that:

A) people tend to behave more morally when they are in a group.
B) people tend to behave more morally when they are alone.
C) people's moral behavior is not influenced at all by cultural norms.
D) there is no disagreement among cultures about what is right and what is wrong.