I hope this message finds you very well;
I do not agree with Answer A, " Most households whose members do any long-distance driving own at least two passenger vehicles." This implies that the number of vehicles, overall, is increased, whereas, an expression such as " two-passenger vehicles" or "two-passengered vehicles" will precisely indicates that the number of two-seated vehicles is increased. In this case, the premise will go with the conclusion (i.e. safer and more efficient).
Could you please expand on this subject matter!
Very Kind Regards