Multi-choice problem: Choose from the options at the end, and answer how do you do this: How to keep the airflow vent on a fan clean from obstruction?

Choices:
-- Purchase a can of concentrated air and carefully place the nozzle just short of the vent, spray until dust is removed.
-- Purchase a can of concentrated air and place the nozzle against the vent, spray until dust is removed.
Purchase a can of concentrated air and carefully place the nozzle just short of the vent, spray until dust is removed.