The Difference Between a Nash Equilibrium and a Subgame-Perfect Equilibrium

The difference between a Nash equilibrium and a subgame-perfect equilibrium is:

A) the former requires rational play both on and off the equilibrium path but the latter requires rational play only on the equilibrium path.
B) the former requires rational play only on the equilibrium path but the latter requires rational play both on and off the equilibrium path.
C) Nash equilibria are a subset of the subgame-perfect equilibria.
D) nothing;they are synonyms.