Alliteration is when two or more words have the same beginning sound. In the poem there are three examples:
1) Though...thy...thou
2) crest...craven
3) shorn...shaven
Alliteration gives the text a more unified rhythm, in a way I guess. It makes the piece sound more together.
Hope this helps!
C. The characters reach a decision
He descrover a dead body near the parking lot
It would be imagery because the excerpt is very descriptive.