Which of the following statements is true regarding the variance or standard deviation of a portfolio of two risky securities? a. The degree to which the portfolio variance is reduced depends on the degree of correlation between securities. b. There is a linear relationship between the securities' coefficient of correlation and the portfolio's standard deviation. c. If the two securities are perfectly negatively correlated, the minimum variance portfolio has a standard devaition that is d. The portfolio variance is independent of the correlation between securities. e. If the two securities are not correlated, the minimum variance portfolio has a standard devaition that equals zero