Final answer:
Option a) "I celebrate myself, and sing myself," from Walt Whitman's "Song of Myself," is the best example of alliteration among the provided choices, with the repetition of initial 's' sounds creating a unifying rhythm.
Step-by-step explanation:
The best example of Walt Whitman's use of alliteration to unify his ideas from the provided quotations is a) "I celebrate myself, and sing myself". This line from "Song of Myself" in Leaves of Grass exhibits alliteration with the repetition of the initial 's' sound in 'celebrate' and 'sing' and 'myself.' Alliteration is a poetic device that involves the repetition of the same initial consonant sound in closely positioned or adjacent words. Whitman's use of alliteration in this line creates a musical rhythm that emphasizes the act of self-celebration and self-expression, which are central themes in his poetry.
The other options do not exhibit alliteration as clearly as option a). Option b) "The learned and the unlearned" does not repeat consonant sounds at the beginning of closely positioned words. Option c) "Afoot with my vision" and option d) "And all I see multiplied as high as I can cipher" also lack this repetition, meaning they don't display alliteration the way the first option does.