Which of the following best explains why the labor supply curve slopes​ upward?
A. When the price of a good​ increases, firms get more value out of each worker and thus seek to hire more workers.
B. When the output that a firm produces​ increases, the opportunity cost of hiring another worker increases.
C. When wages​ increase, the opportunity cost of not working​ increases, leading people to seek more work hours.
D. When the wage rate​ increases, the number of employees that a firm wants to hire increases.