Concept:A sonnet that has a final couplet is the English or Shakespearean sonnet, which is built from three quatrains followed by a couplet.Explanation:The English sonnet consists of three quatrains and a final rhyming couplet.Its rhyme scheme is ababcdcdefefgg.The first three quatrains develop an idea, and the final couplet gives a conclusion or turn.Therefore, a sonnet has a final couplet when it has three quatrains.Answer:D. Three quatrains