Read the descriptions of rhyme schemes below.

free verse: poetry that does not use a consistent rhyme scheme
iambic pentameter: a poetic rhyme scheme in which each rhyming line has ten syllables
blank verse: poetry that uses unrhymed iambic pentameter
rhyming couplets: a series of two consecutive lines that rhyme in a poem
based on the descriptions, what rhyme scheme does the poem "harlem" use?

a. free verse
b. iambic pentameter
c. blank verse
d. rhyming couplets

The poem "Harlem" uses A. free verse

Explanation:

First, let's take a look at the poem "Harlem" by Langston Hughes:

What happens to a dream deferred?

     Does it dry up

     like a raisin in the sun?

     Or fester like a sore—

     And then run?

     Does it stink like rotten meat?

     Or crust and sugar over—

     like a syrupy sweet?

     Maybe it just sags

     like a heavy load.

     Or does it explode?

We can clearly see there isn't much of a pattern being applied. The very fist line of the poem is much longer than the rest of it. None of the lines constitute a iambic pentameter - a five-time repetition of an unstressed syllable followed by a stressed one. Therefore, we can eliminate options B and C, according to the descriptions provided in the question.

We can safely eliminate letter D as well, since we do not have a pattern of two consecutive lines that rhyme in this poem -- note that the two last lines do rhyme and are consecutive in the sense that there isn't another line between them; still, they do not belong to the same stanza and are not related enough to be considered a couplet.

The only option left, and the correct one is A. free verse. Even though there are a few rhymes taking place in "Harlem" (sun/run, meat/sweet, load/explode), they do not follow a consistent pattern. Mostly, they are intercalated with lines that do not rhyme at all (up, sore, over, and sags). There is no concern for metrics either, each line having a different number of syllables.