Originally posted by HeideggerNb3 seems to be the most common. Be3 and Nc3 are both playable as well (after 5. Nc3 Qb6 you can play 6. Be3, or 6. Na4 Qa5+ 7. c3).
After the white knight takes the black pawn,1. e4 c5 2. Nf3 e6 3. d4 c5xd4 4. Nf3xd4 Bc5, what do you do when black bishop comes out to threaten knight, with his queen also going to come out?