Alpha Sold Machinery, Which It Used in Its Business, to Beta

Alpha sold machinery, which it used in its business, to Beta, a related entity, for $40,000.Beta used the machinery in its business. Alpha bought the machinery a few years ago for$50,000 and has claimed $30,000 of depreciation expense. What is the amount and character of Alpha's gain?

A) $20,000 ordinary gain.
B) $20,000 ordinary income under §1239.
C) $20,000 capital gain.
D) $10,000 ordinary gain and $10,000 §1231 gain.
E) None of the choices are correct.