4. Buzz Corporation sold an office building that it used in its business for $500,000. Buzz originally purchased the building for $650,000 and has taken $200,000 of depreciation on asset. What is the amount and character of Buzz's gain or loss?

A. $50,000 Sec. 1231 gain B. $50,000 ordinary gain C. $10,000 ordinary gain, $40,000 Sec. 1231 gain D. $40,000 ordinary gain, $10,000 Sec. 1231 gain E. None of the choices are correct

Answer is C. but please explain why, thanks.