Chess Opening Theory/1. e4/1...c6/2. Bc4/2...d5

White has two options:

3. exd5 cxd5 is the more common move in the Lichess database. However, after the pawn trade, White will be down a tempo and a center pawn with little to show for it. 4. Bb5+ can be blocked by the opposing bishop, and if White trades, Black is comfortable. 4. Bb3 keeps a bishop on the f7 diagonal, but does not challenge much.

3. Bb3 gambits White's e4 pawn in order to gain a tricky, if somewhat dubious, attack. Note that after 3...dxe4 4. Qh5, Scholar's Mate is not threatened yet (after, say, 4...Nf6?! 5. Qxf7+, the king can move to d7), though the f7 pawn is still vulnerable.

Any other move loses the bishop or makes the initial 2. Bc4 a waste of time.