Answer:
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.
      <em>Or does it explode?</em>
<em />
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.
<u>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.</u>