Which one of the following is true? Given an investment opportunity set and the risk free rate, investors may choose to invest in any portfolio on the investment opportunity (that lies above the minimum variance portfolio), and his/her choice is determined by to his/her risk preference. The single factor model assumes that each security comoves with other individual securities as well as the market index. Minimum Variance portfolio has the best reward to risk ratio among all portfolios along the investment opportunity set. Given an investment opportunity set, investors should not invest in any portfolio that lies below the minimum variance portfolio