Chess Opening Theory/1. e4/1...Nf6/2. e5/2...Nd5/3. c4/3...Nb6/4. d4

=Alekhine's Defence= White has occupied the center with pawns. From here, white can choose how to reinforce his pawn structure.

Theory table
1.e4 Nf6 2.e5 Nd5 3.c4 Nb6 4.d4