The Queen's Gambit is an effective chess opening whereby white sacrifices a pawn on c4 in order to take control of the center of the board. This is not a true gambit because black typically cannot hold onto its pawn after doing the capture.
An effective response by black is to decline the gambit and instead offer the Albin Countergambit, by moving to d4 and then advancing the original pawn to e4 after white accepts the countergambit. White then often castles kingside.
Another effective response by black is 1.d4 d5 2.c4 ... e6.
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