Which of the following is the best definition for the concept of efficient capital market? Select one: a. The average compound return earned per year over a multi-year period. b. The excess return required from an investment in a risky asset over a risk-free investment. C. A symmetric, bell-shaped frequency distribution that can be defined by its mean and standard deviation. d. The hypothesis is that actual capital markets are efficient. e. Market in which security prices reflect available information