question: bullet:barrel
choices.label: A B C D
choices.text: carriage:mountain road atom:nucleus electric current:cable pedestrian:zebra crossing
explanation: the "bullet" must be fired through the "barrel". one can drive a "carriage" without going through a "mountain road". "atoms" have "nucleus" in their constituent parts. "electric current" must be carried through a "cable". "pedestrians" can also walk without going through "zebra crossings".
relation: bullet barrel R3.10
relation: atom nucleus R2.3
relation: electric current cable R3.10