For a monopsony buyer, the marginal expenditure per unit of an input:

A) exceeds the average expenditure per unit.
B) is less than the average expenditure per unit.
C) equals the average expenditure per unit.
D) any of the above could be true.

In a monopsony, where there is only one buyer for a particular input, the marginal expenditure per unit exceeds the average expenditure per unit. This is because to purchase an additional unit of the input, the monopsonist often has to pay a higher price for all units purchased, not just the additional unit, due to the upward-sloping supply curve they face.