If the security returns can be described by a six-factor model, which of the following statements are true regarding the Arbitrage Pricing Theory? It requires six well-diversified factor-portfolios. As there are many factors, each factor-portfolio does not need to be well-diversified. It requires six factor-portfolios uncorrelated each other. One of the factor portfolios must be equal to the true market portfolio. As there are too many factors, arbitrage opportunities never disappear.