David acquired an automobile for $30,000 for use in his unincorporated business at the beginning of 2023 and used the standard mileage rate method in 2023. He plans to switch to the actual expense method for 2024. The automobile was used 25,000 miles for business purposes in 2023. What is the amount of the adjusted basis of the automobile for purposes of computing depreciation in 2024?

A) $21,000 B) $30,000 C) $21,500 D) $16,000