3. Which of the following statements is incorrect?

(a) In both U.S. and Australia, female workers on average earn less than male workers.

(b) In the U.S., female workers with a college degree on average earn less than male workers with a college degree.

(c) In the U.S., female workers without a college degree on average earn less than male workers without a college degree .

(d) In the U.S., unemployment rate of the black population is slightly lower than the unemployment rate of the white population. However, the average earnings of the black population is lower than the average earnings of the white population