Please choose the correct ending to complete the given sentence: Assembling bicycle: He starts off by turning the axle of the wheel with a pair of tongs to position the axle in the center. Then he fixes the center nut and uses a wrench to loosen it. then he

Ending1: moves back and forth and finishes. Ending2: tightens the nuts with a tool. Ending3: adjusts the torque to make the motor crank even bigger. Ending4: uses his hands to remove the axle out.

Answer format: ending1/ending2/ending3/ending4