Which of the Following Transactions Adds to U

Which of the following transactions adds to U.S. GDP for 2010?

A) In 2010, Ashley sells a car that she bought in 2006 to William for $5,000.
B) An American management consultant works in Mexico during the summer of 2010 and earns the equivalent of $30,000 during that time.
C) When John and Jennifer were both single, they lived in separate apartments and each paid $750 in rent. John and Jennifer got married in 2010 and they bought a previously unoccupied house that, according to reliable estimates, could be rented for $1,600 per month.
D) None of the above transactions adds to U.S. GDP for 2010.