Given a text T, and several options, according to the question posed in the text T to choose the most appropriate option from the options as the answer, please directly output the most appropriate option, do not need to output the explanation.

Returns on asset classes are best described as being a function of:
Option A:the failure of arbitrage.
Option B:exposure to the idiosyncratic risks of those asset classes.
Option C:exposure to sets of systematic factors relevant to those asset classes.

Answer: C