instruction:
You are given an elementary science question along with a few answer options. List all the words from the question that are essential and sufficient for choosing the correct answer option. Keep in mind that essential words are necessary to understand the meaning of the given question. However, non-essential words provide little information needed to select the correct answer. You can think about it like this: If the question was in another language, knowing the meaning of which words were necessary and enough for you to understand the question and answer it?. If your answer consists of multiple spans of words from the question, separate those using a comma (", "). Do not generate any word that is not present in the question. Make sure that your response is contained in the given question and the words are in the same order as the question.
 Grammatical correctness is not important.
question:
Question: John was using his mp3 player when it suddenly stopped working. What is the first thing John should do to try correcting the problem? (A) recharge the battery (B) take the player apart (C) replace the player with a new one (D) change to a different song?
answer:
mp3, player, stopped, working., first, correcting, problem?


question:
Question: Which of the following has the greatest potential energy? (A) Potential energy always stays constant. (B) A roller coaster car in the middle of the hill (C) A roller coaster car nearing the bottom of the hill (D) A roller coaster car at the top of the hill?
answer:
greatest, potential, energy?


question:
Question: Northern forests have evergreen trees and large animals like deer and bears. Some nonliving things that make an ecosystem like this are ___. (A) climate and soil type (B) houses and cars (C) rocky terrain and ice (D) nearby towns and cities?
answer:

Northern, forests, evergreen, trees, large, animals, nonliving, things, make, ecosystem