Which of the Following Is an Example of Labor-Market Discrimination

Which of the following is an example of labor-market discrimination?

A) A man who makes 5 widgets an hour is paid a higher wage than a man who makes 2 widgets an hour.
B) Tim and Alexis are equally popular and productive bartenders but Tim makes $2 per hour more than Alexis.
C) Minorities are accepted into college at lower rates than non-minorities.
D) Only workers with college degrees are interviewed for a job as a high school science teacher.
E) Hannah works at an ice cream shop and makes more money in tips than Hillary because Hannah is nicer to the customers.