question: what causes metal to be orange on the surface?
choices.text: melanin content gold antigens air pollution electrons conductors melanin amount iron oxide
choices.label: A B C D E F G H
fact2: Iron oxide is rust .
combinedfact: when a metal contains iron oxide, it becomes orange on the surface
formatted_question: what causes metal to be orange on the surface? (A) melanin content (B) gold (C) antigens (D) air pollution (E) electrons (F) conductors (G) melanin amount (H) iron oxide