Sonic's Secrets: Aero the Acro-Bat 2.

To access the Level select screen you must first activate the cheat mode. On the Options screen (see right) use Sound Test to play sounds:

8, 4, 19, & 71.

The screen will flash confirming that you have entered the code correctly.

Once the game has started you can access the level select screen at any time by pausing the game (press Start) then pressing and HOLDING:

Down + A + C (Together)

Until the level select menu appears (see right).