Consider historical data showing that the average annual rate of return on the S&P 500 portfolio over the past 85 years has averaged roughly 8% more than the treasury bill return and that the S&P 500 portfolio has incurred losses in only 20 of those 85 years. If an investor wishes to maximize returns while minimizing risk, Which of the following investment options would be the most suitable?
a) Investing solely in the S&P 500 portfolio
b) Investing solely in treasury bills
c) Diversifying investments between the S&P 500 portfolio and treasury bills
d) Investing in high-risk, high-return assets outside of the S&P 500 portfolio and treasury bills