Final answer:
Schubert's "Erlkönig" is in a through-composed form, which means the music changes throughout to closely follow the narrative and emotions of the text.
Step-by-step explanation:
In Franz Schubert's art song "Erlkönig," he employs a composition structure where a new form is presented for each verse. This approach is called through-composed. In contrast to strophic form, where the same melody is repeated with every stanza or verse, through-composed songs feature continuously varying music that follows the narrative of the text closely. Therefore, the main answer to the question is: B. Through-composed. This technique allows the music to reflect the dramatic shifts within the storyline, enhancing the listener's experience by aligning the musical expression with the emotions and actions conveyed through the lyrics.