question: brain:heart
choices.label: A B C D
choices.text: head:human body steering wheel:engine commander:army nerve:serum
explanation: human body has "brain" and "heart". Both the "brain" and "heart" belong to organs. the "head" is part of the "human body". Car has "steering wheel" and  "engine". Both the "steering wheel" and the "engine" belong to the auto parts. "commander" command "army". there is no obvious logical relationship between "nerve" and "serum".
relation: brain heart R2.4
relation: head human body R2.3
relation: steering wheel engine R2.4
relation: commander army R4.4