Best response to the Queen's Gambit Accepted: Classical Defense, Normal Line (D26)

1. d4 d5 2. c4 dxc4 3. Nf3 Nf6 4. e3 e6 5. Bxc4 c5 6. O-O · Black to move

What is the best response to the Queen's Gambit Accepted: Classical Defense, Normal Line (1. d4 d5 2. c4 dxc4 3. Nf3 Nf6 4. e3 e6 5. Bxc4 c5 6. O-O)? Black to move. See the top replies ranked by opening theory and real-game results, starting with Nc6.

The main theoretical reply is Nc6, reaching the Queen's Gambit Accepted: Classical Defense, Steinitz Variation, Development Variation.