The last one is the answer
D. It's very vague. isn't as articulate as the others
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.