Answer: B) the feeling of repeated melancholy.
Step-by-step explanation: In the given lines from the poem "Dover Beach" by Matthew Arnold, we can see the description of a feelling of melancholy (a gloomy state of mind, pr a feeling of pensive sadness, typically with no obvious cause) we can see that in the lines "With tremulous cadence slow, and bring The eternal note of sadness in, also we can see that this feeling repeats ("Begin, and cease, and then again begin") so the mood is a feeling of repeated melancholy.