The first of the two (5… e6) is the more solid one, where Black’s goal is to develop his kingside as fast as possible. Players of White have tried several moves against that setup, and 6. Na3 seems like the most ambitious one. The game can continue with 6… Nc6 7. Be3 cxd4 8. Nb5 Qd7 9. Nbd4 Nd5, and Black’s position should be fine.
With 5… Bg4 Black wants to develop his light-squared Bishop before completing his development on the kingside with e7-e6, Be7 and O-O. White’s reaction 6. Be2 doesn’t seem to pose real problems for his opponent, but 6. dxc5 does requires precise play from Black. After 6. dxc5 Qxc5 7. Na3 a6 8. Be3 Qc7 9. h3 Bh5 10. Qa4+ Nbd7 Black should not be worse.
[Diagram: Black to Move] This is a well-known trick that has appeared even in a few grandmaster games. White has just played Qd1-a4, and the Black Queen is under attack. How should Black react?
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