Final answer:
The key signature for A♭ Major has four flats including B♭, E♭, A♭, and D♭, so the correct answer is A♭.
Step-by-step explanation:
The key signature for A♭ Major has four flats: B♭, E♭, A♭, and D♭. Therefore, the correct answer to which key signature it is would be option 1) A♭. It's important to note that while C♭ Major is enharmonically equivalent to B Major, it is not typically used due to its complexity, and Concert B is not a key signature but a reference pitch used primarily in transposing instruments.