question: trees:coal
choices.label: A B C D
choices.text: gasoline:petroleum ivory:elephant resin:amber sun:energy
explanation: "trees" are the raw materials of "coal", which requires "trees" to undergo chemical changes after being buried for tens of millions of years. "petroleum" is the raw material for "gasoline", but it does not chemically change itself "ivory" is a part of "elephant", but "ivory" is not the raw material of "elephant" "resin" is the raw material of "amber", which requires "resin" to undergo chemical changes after being buried for tens of millions of years. Solar energy can be formed by nuclear fusion reaction inside the "sun". Solar energy is a kind of "sun", but "sun" is not a raw material
relation: trees coal R3.7
relation: gasoline petroleum R3.7
relation: ivory elephant R2.3