Which of the following is the best example of a gender stereotype (rather than some other form of gender bias)?

a. An accounting firm has an unwritten policy that the more challenging projects should be given to men instead of women.
b. A friend believes that women are not aggressive enough to be good politicians.
c. A neighbor says that he doesn't like female science teachers.
d. A clerk at a store ignored two women who were standing in line, and he started helping a man who was behind them in line.

B