Please choose the correct ending to complete the given sentence: Doing motocross: A biker seated on a bike revs the engine. another biker

Ending1: is shown seated on a bike, making a gesture with both arms. Ending2: approaches him, helping him mount to his bike. Ending3: comes on. Ending4: walks down the track above the track.

Answer format: ending1/ending2/ending3/ending4