The CAPM assumes that all investors will hold the same portfolio of risky assets. With respect to borrowing at the risk-free rate and on short selling, investors may hold very different portfolios:
　　A. under no circumstances.
　　B. if there are restrictions on borrowing at the risk-free rate but not on short selling.
　　C. if there are restrictions on short selling but not on borrowing at the risk-free rate.
　　D. if there are restrictions on both borrowing at the risk-free rate and/or short selling.
　　Answer:D
　　Restrictions on short selling and/or borrowing at the risk-free rate make investors construct portfolios with considerably different compositions.