Question

Realism was a response to a0.

Answer 1

Realism was a response to Romanticism

Answer 2

Realism is a literary movement that was created in response to romanticism.  Romanticism had at its basis—like the name suggests—a romantic (almost too optimistic) notion of all about which was written.   Realism, on the other hand, was just the opposite in that it portrayed society (reality) as the way it really was almost pessimistically (or at least as it was seen by the author) and can be seen as an equal and opposite reaction to romanticism.