Suppose a Firm Overpays Its Workers at the Start of the Job

Suppose a firm overpays its workers at the start of the job, and then the firm slowly lowers wages over time until eventually the firm pays the workers considerably less than the worker's marginal product of labor. What prevents this "reverse of a delayed-compensation scheme" from being implemented?

A) Workers prefer wages to increase over time.
B) The firm would fire the worker as soon as the worker's value of marginal product exceeded the worker's wage.
C) Workers would leave the job as soon as the firm tries to pay the worker less than his or her value of marginal product.
D) The firm would need to enforce a mandatory retirement age which is illegal in the United States.
E) The workers would never have an incentive to invest in general training.