A Sonnet has a final couplet when it has___________

Analyze the question: It asks which structure of a sonnet ends with a final couplet (two rhyming lines).

Explain the concept: There are two main types of sonnet:

1. Petrarchan (Italian) sonnet: 14 lines divided into an octave (8 lines) and a sestet (6 lines). The sestet is usually rhymed cde cde or cdcdcd, and it does not normally end in a couplet.
2. Shakespearean (English) sonnet: 14 lines divided into three quatrains (3 x 4 = 12 lines) followed by a final rhyming couplet (2 lines). Rhyme scheme: abab cdcd efef gg.

Step-by-step solution:

• A: A sestet belongs to the Petrarchan form, whose last six lines don't necessarily end in a couplet. ✗
• B: An octave is the first 8 lines of a Petrarchan sonnet. ✗
• C: Two sestets would be 12 lines, which is not a sonnet structure. ✗
• D: Three quatrains give 12 lines, and the remaining 2 lines form the final couplet, which is exactly the Shakespearean sonnet. ✓

Answer: D. Three quatrains

Tip: Remember "3 + 1": 3 quatrains + 1 couplet = Shakespearean. And "8 + 6": octave + sestet = Petrarchan. If you see "couplet" in a sonnet question, think Shakespeare!