6. One of the main problems with the arbitrage pricing theory is __________.

a) its use of several factors instead of a single market index to explain the risk-return relationship

b) the introduction of nonsystematic risk as a key factor in the risk-return relationship

c) that the APT requires an even larger number of unrealistic assumptions than does the CAPM

d) the model fails to identify the key macroeconomic variables in the risk-return relationship

e) None of these answers are correct.