What is the main advantage of using helical gears instead of spur gears?

Helical gears are designed with teeth that are cut at an angle to the axis of the gear, which allows for engagement of the teeth to occur gradually. This gradual engagement results in a more constant and smoother flow of power between the gears, leading to a quieter operation compared to spur gears, which engage all at once. The slanted teeth of helical gears help to distribute the load over a larger contact area, reducing vibrations and noise levels during operation. This feature makes helical gears particularly advantageous in applications where noise reduction and smooth performance are priorities. The other options, while they have their merits, do not accurately represent the primary benefit of helical gears as concisely as the aspect of smoother and quieter operation does.