[
  {
    "sentence": "_____ libro está en la mesa.",
    "correct": "El",
    "distractor": "La",
    "explanation": "libro ends in -o → masculine → el.",
    "source_chapter": "04",
    "source_title": "Articles"
  },
  {
    "sentence": "Voy a _____ piscina.",
    "correct": "la",
    "distractor": "el",
    "explanation": "piscina ends in -a → feminine → la.",
    "source_chapter": "04",
    "source_title": "Articles"
  },
  {
    "sentence": "_____ problema es difícil.",
    "correct": "El",
    "distractor": "La",
    "explanation": "Greek-origin -ma noun → masculine: el problema.",
    "source_chapter": "04",
    "source_title": "Articles"
  },
  {
    "sentence": "Tengo _____ libro nuevo.",
    "correct": "un",
    "distractor": "uno",
    "explanation": "Before a masculine noun use un, not uno.",
    "source_chapter": "04",
    "source_title": "Articles"
  },
  {
    "sentence": "_____ ciudad es grande.",
    "correct": "La",
    "distractor": "El",
    "explanation": "Nouns ending in -d are usually feminine.",
    "source_chapter": "04",
    "source_title": "Articles"
  },
  {
    "sentence": "Bebo _____ agua fría.",
    "correct": "el",
    "distractor": "la",
    "explanation": "agua takes el in the singular (stressed initial a-) even though it's feminine.",
    "source_chapter": "04",
    "source_title": "Articles"
  },
  {
    "sentence": "Quiero ver _____ foto.",
    "correct": "la",
    "distractor": "el",
    "explanation": "foto is short for fotografía → feminine.",
    "source_chapter": "04",
    "source_title": "Articles"
  }
]