Which of the following is a TRUE statement of modern portfolio theory?

a) It shows how to form portfolios with the highest possible expected rate of return for any given level of risk.

b) It stipulates that investors should diversify their investments so as to be unnecessarily exposed to a single negative event.

c) It states that securities should be managed within a portfolio, rather than individually, to lower risk-reduction gains.

d) It demonstrates that by combining securities into portfolios, we can increase risk.