The option which describes the structure of a Shakespearean sonnet is " three quatrains and a couplet." Answer A is correct.
Shakespeare's sonnets are written in a meter denominated iambic pentameter, a rhyme scheme in which each sonnet line is made up of ten syllables. The syllables are split into five pairs known as iambs or iambic feet. An iamb refers to a metrical unit consisting of one unstressed syllable followed by one stressed syllable.