{
  "correct_letter": "B",
  "correct_formula": "ΣF_ext = 0",
  "annotation": "Environment: g=-9.81, F_drag=0.0",
  "choices": [
    "ΣF = m·Δv / (Δt·cosθ)",
    "ΣF_ext = 0",
    "T = 2π·√(m/k)",
    "F_drag = (1/2)·C_d·ρ·A·v²"
  ],
  "correct_index": 1,
  "physics_type": "AtRest",
  "seed": "AtRest|benchmark/at_rest/0"
}