Final answer:
The primary purpose of the couplet in this sonnet is to add a twist to the ideas about time described in the three quatrains. The correct answer is option C.
Step-by-step explanation:
The primary purpose of the couplet in this sonnet is to add a twist to the ideas about time described in the three quatrains. The couplet serves as a conclusion or resolution to the themes and ideas presented in the rest of the poem. It emphasizes the speaker's desire for his love to become famous and live forever, contrasting with the passage of time. By achieving fame through poetry, the speaker believes they can defy the decay of time.