The answer is: a noun.
A noun is a word that names a particular thing or a set of things. Nouns are classified in many ways, but for clarity purposes, it can be said that the two more general forms of the noun are the proper noun (which refers to unique entities, like Europe or John) and the common noun (which refers to a class of entities, like neighborhood or country).
According to countless methods which different authors use in poetry, I am pretty sure that the main point that is as important as content in any poem is b. figurative language (which means that author contributes with his own style of writing so that you can identify him from the others). You may think that the right answer is sound, but do not forget about many types of blank verse, especially those when it is really difficult to read not only because there is no rhyme.
The answer is A for showing language