question: You are answering a 3D spatial-reasoning question from a SINGLE monocular driving image with numbered bounding boxes. Frontier models routinely get these right by luck while reasoning incorrectly: they lean on flat-image shortcuts ('lower in the frame = closer', 'bigger box = nearer', 'left in the image = to my left') that collapse on elevated roads, slopes, curves, and intersections. To answer reliably you must reconstruct the real 3D scene, not the pixel layout. Reason explicitly and quantitatively.
  
  Question: Compare the heading direction of object <2> with object <4>. Pick the option that best describes the relationship.
  
  Reasoning protocol (metric 3D):
  1. Determine EACH object's heading separately from its visible faces (rear/front/flank), light positions, wheel angle, and lane direction — never from image position.
  2. Express each heading relative to the ego forward axis.
  3. Take the angular difference: ~0 deg = same direction, ~180 deg = opposite, ~90 deg = perpendicular. State both headings and the difference before answering.
  
  Finish with a single line in the exact format: 'Answer: <LETTER>'.
choices: A. cannot be determined B. perpendicular to each other C. roughly opposite directions D. roughly the same direction