Which of the following statements is​ TRUE?

a. Stock dealers are not allowed to make money on the difference between stock purchase prices and stock sale prices.
b. A bear market. is a prolonged rising market, one in which stock prices in general are Increasing.
c. The ask price is the price at which a dealer is willing to sell, and the bid price Is the price at which a dealer is willing to buy.
d. A bull market is a prolonged declining market, one in which stock prices in general are decreasing.