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.

Ex Input:
Question: When a goldfish is breathing, what is it taking in? (A) Oxygen (B) Carbon Dioxide (C) nitrogen (D) glucose?

Ex Output:
goldfish, taking, in?


Ex Input:
Question: Which would be the best tool to measure the volume of a rock? (A) Meter stick (B) Empty graduated cylinder (C) Graduated cylinder with water (D) Triple beam balance?

Ex Output:
tool, measure, volume, rock?


Ex Input:
Question: What happens to an organism that has no special characteristics suited for adaptation to its environment? (A) The other organisms will help it survive. (B) It will change the environment it lives in. (C) It will stop reproducing until conditions are favorable. (D) It will have difficulty surviving or will not survive at all.?

Ex Output:

organism, characteristics, suited, adaptation, environment?