Helen's Cat Fluffy Has Run Away, and She Places Reward

Helen's cat Fluffy has run away, and she places reward posters throughout her neighborhood. Mark sees one of the reward posters and spends the next six hours searching for Fluffy. While Mark is searching the neighborhood, Fluffy gets hungry and comes home.

A) This is a bilateral contract, and Mark is entitled to be compensated for his efforts.
B) This is a bilateral contract, and Mark is entitled to nothing because he didn't perform.
C) This is a unilateral contract, and Mark is entitled to be compensated for his efforts.
D) This is a unilateral contract, and Mark is entitled to nothing because he didn't perform.