The Landlord's Cost of Continuing to Rent a House to Smith

The landlord's cost of continuing to rent a house to Smith is

A) the maintenance cost on the house (a constant under all options) .
B) the maintenance cost plus depreciation on the house.
C) zero, since the construction costs of the house are sunk costs.
D) the revenue foregone as the result of not renting to the highest bidder other than Smith.