Eileen Dover announces she plans to become a mime. Her friend, Paul Down, who cannot bear the sight of mimes, offers to pay Eileen Dover $500 if she agrees never to become a mime. Paul Down's promise is: 

Enforceable because each side offered legally sufficient consideration to form a contract 

Not enforceable because Eileen Dover never made any enforceable promise to Paul Down 

Not enforceable because Eileen Dover had no right to become a mime 

Not enforceable because Eileen Dover voluntarily chose not to become a mime 

Enforceable because Eileen Dover agreed to refrain from doing something she was legally entitled to do