Which statement about portfolio diversification is correct?
a. Proper diversification can reduce or eliminate systematic risk.
b. Diversification reduces the portfolio's expected return because it reduces a portfolio's total risk.
c. As more securities are added to a portfolio, total risk typically can be expected to fall at a decreasing rate.
d. The risk-reducing benefits of diversification do not occur meaningfully until at least 30 individual securities are included in the portfolio.