Chess Opening Theory/1. e4/1...c5/2. b4/2...cxb4/3. a3/3...d5

3...d5!
This is the antidote to the Wing Gambit. Black counterattacks in the center and prevents axb4 due to dxe4, winning a central pawn. White cannot win the pawn back with 4. exd5 Qxd5 5. axb4?? due to 5... Qe5+.