William and Mary have owned an apartment building since 2014. They paid $120,000 for the building. In 2020, they put on a new roof that cost $8,000. They must: 

a. Add the $8,000 to the $120,000 cost and depreciate the total.

b. Subtract the $8,000 from their rental income as an expense.

c. Start depreciating the roof in 2020 as a separate property item.

d. Depreciate the roof as a separate item placed in service in 2013.

e. None of these