Assume all investors want to hold a portfolio that, for a given level of volatility, has the maximum possible expected return. Explain why, when a risk-free asset exists, all investors will choose to hold the same portfolio of risky stocks. (Select the best choice below.) A. All investors will do the same thing-that is, they will minimize their volatilities-so they will all hold the same portfolio. B. All investors will do the same thing-that is, they will maximize their expected returns-so they will all hold the same portfolio. C. Investors who want to maximize their expected return for a given level of volatility will pick portfolios that maximize their Sharpe ratio. The set of portfolios that does this is a combination of a risk-free asset and a single portfolio of risky assets-the tangential portfolio. D. When a risk-free asset exists, it provides a safe investment opportunity. Given this safe investment opportunity, investors who maximize their expected returns for a given level of volatility will pick the same expected return and, hence, the same portfolio