question: iron:rust
choices.label: A B C D
choices.text: quicklime:calcium carbonate water:water vapor iron:rust wheat:flour
explanation: "rust" is the oxide of "iron", and "rust" corresponds to "iron". "calcium carbonate" is the product of the chemical reaction between "quicklime" and carbon dioxide, and "calcium carbonate" is not an oxide. "water vapor" is the gaseous "water", not the oxide of "water". "rust" is iron oxide, which is the oxide of "iron", and "rust" corresponds to "iron". "flour" is the processed product of "wheat", and "flour" is not an oxide of "wheat".
relation: rust iron R3.10
relation: calcium carbonate quicklime R3.10
relation: water vapor water R3.10
relation: rust iron R3.10