Security analysts are professionals who devote full-time efforts to evaluating the investment worth of a narrow list of stocks. For example, one security analyst might specialize in bank stocks while another specializes in evaluating firms in the computer or pharmaceutical industries. The following variables are of interest to security analysts (Radcliffe, Investments: Concepts, Analysis and Strategy, 1994). Which are discrete and which are continuous random variables?

a. The closing price of a particular stock on the New York Stock Exchange

b. The number of shares of a particular stock that are traded each business day

c. The quarterly earnings of a particular firm

d. The percentage change in yearly earnings between 1999 and 2000 for a particular firm

e. The number of new products introduced per year by a firm

f. The time until a pharmaceutical company gains approval from the U.S. Food and Drug Administration to market a new drug