choices.label: A B C D
choices.text: iron:soil grass:tree cold:fever clothes:pants
explanation: "ice" and "fog" are different forms of the same substance, and both "ice" and "fog" are natural objects. "iron" and "soil" are not different forms of the same substance, and "iron" is not a natural object. "grass" and "tree" are both plants, and "grass" and "tree" are both natural objects. both "cold" and "fever" are diseases, and neither "cold" nor "fever" is a natural object. "clothes" is a kind of "pants", and neither "clothes" nor "pants" is a natural object.
relation: ice fog R2.4
relation: grass tree R2.4
relation: fever cold R2.4
relation: pants clothes R2.2