Correct Option: D

On January 7, 2013, President Barack Obama nominated Chuck Hagel to serve as Secretary of Defense. He served as a United States Senator from Nebraska from 1997 to 2009.
Note: President Donald Trump appointed retired Marine General James ‘Mad Dog’ Mattis as the 26th secretary of defence. He would also serve as a member of the National Security Council. He has been holding office since January 20, 2017.