In the third stanza of the poem, “o captain my captain! ” the third line is an example of which element of sound?

stanza 3

my captain does not answer, his lips are pale and still;

my father does not feel my arm, he has no pulse nor will;

the ship is anchor'd safe and sound, its voyage closed and done;

from fearful trip, the victor ship, comes in with object won;

exult, o shores, and ring, o bells!

but i, with mournful tread,

walk the deck my captain lies,

fallen cold and dead.

a. alliteration

b. assonance

c. rhyme

d. rhythm