Which poetic form is structured in three parts: strophe, antistrophe, and epode?

The correct answer is the ode, which is a lyrical form traditionally composed of three parts: the strophe, antistrophe, and epode. This structure allows the poet to develop a theme or emotion. The strophe typically presents a situation or argument, the antistrophe responds or contrasts with that initial idea, and the epode oftentimes offers a resolution or conclusion.

In contrast, the other options present different poetic structures: a sonnet generally consists of 14 lines with specific rhyme schemes, a villanelle features a specific form of 19 lines with a repetitive pattern, and a ballad is typically narrative in nature with a focus on storytelling and may not adhere to a strict structural form like the ode does. Therefore, the ode clearly stands out due to its unique three-part structure.