The thymus is a lobed organ located near the $...A...$ and beneath the $...B...$. The most appropriate combination for $A$ and $B$ is:

• A
  $A-heart; B-breast bone$
• B
  $A-liver; B-ribs$
• C
  $A-heart; B-ribs$
• D
  $A-intestine; B-ribs$