An essay is, generally, a piece of writing that gives the author's own argument.
"Servant to Servants" is a poem that was actually written by Robert Frost and in this poem, the speaker engages herself in an appreciation for her husband. The answer for this would be option D. Hope this answers your question.
C. A teacher claims that student performance has gone down based on school - wide test results
I would probably say that the author used diction to achieve some kind of effect in the first sentence.
A. The teacher stood at the door smiling brightly and welcoming each student to her classroom on the first day of school.
The author's diction, or word choice, in this sentence portrays the teacher as a nice, kind, caring person.