Final answer:
The difference between the structures of Whitman's and Longfellow's poems is that Longfellow maintains a consistent meter, while Whitman's rhythm is variable. The best supporting lines are from Longfellow: Lines 9-12 and Whitman: Lines 3-4.
Step-by-step explanation:
Differences in Poetic Structure
The structure of Whitman's poem is different from that of Longfellow's in that Longfellow keeps the same meter throughout the stanza, whereas Whitman does not. This difference can be observed in the regular rhythmic pattern that Longfellow's stanzas adhere to, as opposed to the free-flowing, variable rhythm of Whitman's poetry.
Supporting Lines from the Passages
The lines that support this answer best are from Longfellow: Lines 9-12; Whitman: Lines 3-4. These excerpts showcase the rhythmic consistency in Longfellow's poem versus the varied rhythm in Whitman's verses.