Can anyone explain why D is correct?

In 2016, Mike Elfred received a $165,000 salary from his employer and generated $39,000 net earnings from self-employment from his small business. Which of the following statements is true? A) Mike owes Social Security tax but not Medicare tax on his $39,000 earnings from his small business. B) Mike owes both the Medicare and Social Security tax portions of self-employment tax on his $39,000 earnings from his small business. C) Mike does not owe any self-employment tax because his salary exceeded the 2016 base amount ($118,500) for federal employment tax. D) Mike owes Medicare tax but not Social Security tax on his $39,000 earnings from his small business. Answer: D