A busy professor needs to decide whether to stay in his office to grade papers for another hour or to go home and go to bed.This is an example of:

A) equity versus efficiency.
B) how one person's spending is another person's income.
C) economic incentives.
D) marginal analysis.

This decision involves comparing the marginal benefits of staying in the office to the marginal costs of doing so (such as lost sleep and decreased productivity the next day). The professor should choose the option where the marginal benefit outweighs the marginal cost. Therefore, the best choice would depend on the individual situation and preferences of the professor.