Final answer:
Cilia are hair-like projections that line various systems in the body and help trap and remove foreign particles before they can cause harm.
Step-by-step explanation:
Cilia are microscopic, hair-like projections on cells that line the respiratory, reproductive, and digestive systems. They have the job of trapping and removing dust, germs, and other foreign particles before they can make you sick. Cilia secrete mucus that traps particles, and they move in a continuous wave-like motion that sweeps the mucus and particles upward toward the throat, where they can be expelled from the body.