Which of these rhetorical devices does Thoreau use here?

Answer:
A is the correct answer.
Explanation:
Parallelism is a rhetorical device in which sentences or phrases are constructed following the same structure (meaning, sound, among others) in order to bring a specific rhythm to sentences. Following the same pattern is a big tool to help reach this goal.
In the excerpt, the author used this literary device since he follows the same structure: subject (he) plus a future tense, in this case, simple future (using will) and a verb in simple form. Rhythm is established in the excerpt using this device.