I think the answer is the first one. 'It gives the poem a somber rhythm.' It tells is that Eden was sad and was grieving. Which makes us feel like the mood is dark and sad. I think it could maybe be a bit of the third answer. 'It makes the poem seem like nature is unkind.' It's first talking about leaves and nature, but then talking about someone grieving. So, that means something had to happen, to affect Eden and put her in the state that she is in. That's what I thought when I read the lines.
