Answer:
The sentence that uses parallel structure is the following one: Sara promised that before her test, she would do nothing but sleep, study, and take notes.
Step-by-step explanation:
Parallel structure, also called parallelism, is the repetition of a chosen grammatical form within a sentence. By making each compared item or idea in your sentence follow the same construction, you create a parallel structure. In the sentence above, all the verbs following the conjunction "but" are in the bare infinitive form as they are related to the modal "would" (do, sleep, study, take notes).