The answer is letter D. William Shakespeare's Sonnet 18 has a structure of fourteen lines in an iambic pentameter with a rhymed couplet at the end. It has a rhyme scheme of abab cdcd efef gg. The first two lines rhyme with the third and fourth lines. The fifth and the sixth lines also rhyme with seventh and eighth lines, so as the ninth and tenth lines with the eleventh and twelfth lines. The thirteenth line rhymes with the fourteenth line, making them a rhymed couplet.
