You own a building that has four possible uses: a cafe, a craft store, a grocery store, and a tools store. The building's value in each use is $$3,000$;$$4,000$; $$5,000$; and $$6,000,$ respectively. You decide to open a grocery store. The opportunity cost of using this building for a grocery store is:

Select one:

a$.$ $$3,000,$ the value if the building is used as a cafe.

b$.$ $$4,000,$ the value if the building is used as a craft store.

c$.$ $$1,000,$ the difference in value if the building were used as a tools store and its actual use.

d$.$ $$10,000,$ the sum of the values if the building is used for a cafe, a craft store, or a tools store.