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　　17.   The market portfolio (M) contains the optimal allocation of only risky asseta and no risky assets. Let the S1 be the Sharpe ratio of this market portflio. There exists a risk-free asset. Initially, an investor is fully (100%) invested in M with a portfolio Sharpe ratio of S1. Subsequently, the investor borrows 30% at the risk-free rate, such that she is 130% invested in the market portfolio(M) where this leverage portfolio has a Sharpe ratio of S2。After the leverage (i.e., borrowing at the riskfree rate to invest +30% in M, is the investor still on the efficient frontier and how do the Sharpe ratios?
　　A.    No (no longer efficient), and S2<S1
　　B.    No,but S2=S1
　　C.    Yes(still efficient),but S2<S1
　　D.    Yes and S2=S1
　　答案：D