Best response to the Center Game Accepted (C21)

1. e4 e5 2. d4 exd4 · White to move

What is the best response to the Center Game Accepted (1. e4 e5 2. d4 exd4)? White to move. See the top replies ranked by opening theory and real-game results, starting with c3.

The main theoretical reply is c3, reaching the Danish Gambit.