A piece of Japanese armor was once used to protect the heads of soldiers. This work has since been replaced by twenty-first century fighting gear, but the original armor is on display in a museum. This change over time is an example of

a once-functional piece of equipment has now become a decorative item.
an artifact that holds physical evidence of the past.
amazing technological advances in Japanese armor.
deterioration of an ancient artifact.

a once-functional piece of equipment has now become a decorative item.