28. The Black-Scholes formula assumes that I) the risk-free interest rate is constant over the life of the option. II) the stock price volatility is constant over the life of the option. III) the expected rate of return on the stock is constant over the life of the option. IV) there will be no sudden extreme jumps in stock prices (a) (b) (c) (d) I and II I and III II and III I, II and IV