Answer:
The dreariness of the speaker’s life away from Innisfree.
Explanation:
The lines 'While I stand on the roadway, or on the pavements grey, I hear it in the deep heart’s core' refer to a feeling of closeness to and remembrance of a place dear to the speaker’s heart. There is an implicit sense of removal, of physical distance, contrasted to an emotional proximity.
So we know it reflects his life away from the idyllic Innisfree. Futhermore, the general tone of the phrase, the depiction of the pavements' colour (rather a dull one), appear to suggest a certain general dreariness.
Nick calls Tom and Daisy “careless people” because he recognizes them as selfish, insensitive individuals who take advantage of people and retreat back into their money without accepting responsibility for their actions. After spending time with the Buchanans, Nick is appalled by their lifestyle and reckless decisions.
To snow.
Why? "It's beginning to snow." makes the most sense. "It's beginning snowing." doesn't make as much sense.
