Answer:
The caged bird's song.
Step-by-step explanation:
Maya Angelou's poem "Caged Bird" tells the metaphorical position of the black people as birds kept in a cage, devoid of any freedom. The poem became a huge success, with its referencing to the freedom and rights of the slaves/colored people as compared to those of the whites.
Though there is no specific rhyme scheme in the poem, there are still some instances of the poem having end rhymes with vowel sounds and some cases of assonance. The use of rhyme in the poem is the attempts of the poet to lay emphasis on the song sung by the "caged bird". The caged bird, as a representation of the blacks, sings a song of imprisonment, devoid of liberty and freedom and made to suffer unlike the 'free bird'.
The repetition of the third stanza in the last stanza brings back the focus of the poem, giving it greater importance. Also, there are a lot of rhyming in these lines of the third and last stanzas.
with a fearful trill
of things unknown
but longed for still
and his tune is heard
on the distant hill
for the caged bird
Thus, the correct answer is that the poet uses rhyme to emphasize the caged bird's song.