I would say this group of lines illustrates the music of autumn, because the word choir is mentioned:
<span>"Then in a wailful choir the small gnats mourn
Among the river sallows, borne aloft
Or sinking as the light wind lives or dies".</span>
One great example of suspense in the Hobbit is when Bilbo is in Smaug's smoky, gold encrusted lair, trying to find the sparkling cup, without awakening the dragon. A few times, we see the dragon release a puff of smoke, or stir, and Bilbo stops abruptly, than tiptoes forward quietly. There is so much suspense here while we await his fate!!
Pronoun antecedent
I think that's it
hope it helped :)