(A) believes that all investors should optimize their portfolios a la Markowitz. (B), on the other hand, believes that a number of serious challenges exist for A's contention to be correct and has suggested a labor capital component (a la Mayers) to be included. (C), invokes the theory of Rubinstein, Lucas, and Breeden and believes the foundations of A and extensions of B to be incomplete. Comment on each of their assumptions, challenges, and models?