They are antonyms. Pollute and purify are opposite meanings. Pollute means to ruin or make something unclean, while purify means removing the harmful or dirtiness out of something.
I think your answer is going to be D. Congrats on finishing English!
Since diction in writing refers to the choice of words, the answer is A - strategic word choice used in persuasive rhetoric.
The exposition is the very beginning of the story so it should introduce the characters and the setting and maybe introduce a lesson to be learned.
It would be a comprehensive description and explanation of an idea.
