Please choose the correct ending to complete the given sentence: Doing motocross: A bunch of dirt bikes are going around a dirt track racing. all the riders

Ending1: then run back towards the racetrack. Ending2: go over a jump and land smoothly. Ending3: moving in a single file is lined up. Ending4: are lined up and ready, then the start their race.

Answer format: ending1/ending2/ending3/ending4