Which of the following is used to reduce dust in an arena?

Watering equipment is indeed the correct choice for reducing dust in an arena. This method involves applying water to the surface of arenas or other dusty environments, which helps to bind dust particles together and prevent them from becoming airborne. When the surface is damp, the moisture holds the dust down, creating a more stable environment for both people and animals.

The other methods listed do not effectively minimize dust in the same way. For instance, fans generally circulate air, which can exacerbate the problem by kicking dust back into the air instead of controlling it. Hay could potentially be used to absorb some dust, but it is not a practical or effective solution for large spaces. Brooms, while useful for cleaning up, do not prevent dust from rising and can actually stir up dust particles during the sweeping process. Therefore, watering equipment stands out as the most effective and appropriate option for dust control in an arena setting.