{
  "correct_letter": "C",
  "correct_formula": "ΣM_ext = 0",
  "annotation": "Environment: g=9.81, F_drag=!=0",
  "choices": [
    "W = ΔE_k = (1/2)·m·v_t² - (1/2)·m·v_0²",
    "n_1·sinθ_1 = n_2·sinθ_2",
    "ΣM_ext = 0",
    "F_balance = (m_1 - m_2)·g / (cosα + sinβ)"
  ],
  "correct_index": 2,
  "physics_type": "AtRest",
  "seed": "AtRest|NewtonsFirstLaw/AtRest/4",
  "is_realworld": true,
  "dropped_wrong_formulas": [
    "F_drag = (1/2)·C_d·ρ·A·v²"
  ]
}