Concept:Contact lenses are placed directly on the eye and can carry germs or reduce oxygen supply, causing eye infections.Explanation:Contact lenses sit directly on the cornea.This can trap dirt and bacteria against the eye.Wearing them for a long time also reduces oxygen reaching the eye.Poor cleaning or prolonged use can easily lead to infection.Convex, biconcave, and concave lenses are spectacles worn away from the eye, so they do not directly infect it.Answer:A. contact lenses