Chess Opening Theory/1. e4/1...e5/2. Bc4
Bishop's Opening 
2. Bc4 
White targets the weak f7 pawn and keeps the possibility of playing a deadly f2-f4. Unlike in 2. Nf3, Black's e5 pawn is not under attack, giving him a wider range of choice. Black's main worry is the Qh5 threat. That's why he shouldn't play Be7 or Ne7.
The main choice is 2...Nf6, reacting to White's passivity by attacking the e4 pawn and taking the initiative. Moreover, it prevents Qh5.
Black has still the possibility of mirroring White's move with 2...Bc5.
2...Nc6 is playable, although a bit passive.
The Calabrese Countergambit (2...f5) is very sharp, but may be a deadly weapon if mastered correctly.
2...c6, the Philidor Counterattack prepares d5 but is often considered to be too slow.
2...d6 may transpose to Philidors Defence but not necessarily (Black should expect 3. f4).
Theory table 
1. e4 e5 2. Bc4
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- Batsford Chess Openings 2 (1989, 1994). Garry Kasparov, Raymond Keene. ISBN 0-8050-3409-9.