Which of the following is not a proper adjustment to the basis of property once the orginal basis is determined?

a. Add improvements and betterments

b. Subtract depreciation allowed or, if no depreciation was claimed, the depreciation that was allowable.

c. Subtract other capital recoveries such as deductable casualty losses

d. Add repairs and maintenance expenditures exeeding 15 percent of the cost of the asset within a single year