question: paper:grass
choices.label: A B C D
choices.text: gunpowder:saltpeter magnet:stone bark:cells soy sauce:broad beans
explanation: "grass" is one of the raw materials of "paper", but it is not a necessary raw material for making "paper". the main raw material for making "gunpowder" is "saltpeter", which is an essential raw material for making "gunpowder". "magnet" is a kind of "stone", and "stone" is not the raw material of "magnet". "cells" are part of a "bark", and they are not the raw material of a "bark". "broad bean" is one of the raw materials of "soy sauce", but it is not a necessary raw material for making "soy sauce".
relation: paper grass R3.7
relation: saltpeter gunpowder R3.7
relation: magnet stone R2.2
relation: bark cells R2.3
relation: soy sauce broad beans R3.7