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.

Input: Consider Input: Question: Communities of organisms form part of an organized and balanced ___. (A) population (B) habitat (C) living space (D) ecosystem?

Output: Communities, organisms, form, organized, balanced


Input: Consider Input: Question: Which tool would a student use to measure wind speed? (A) compass (B) barometer (C) anemometer (D) weather vane?

Output: tool, measure, wind, speed?


Input: Consider Input: Question: A factory owner wants to be sure that he does not pollute the air during the manufacturing process. What is a good way to make sure he is not polluting the air? (A) Recycle the water used during the manufacturing process. (B) Swab the machines to test for any oily residues. (C) Test samples of smoke coming from the factory's smokestacks. (D) Use only bottled water in the manufacturing process.?


Output: pollute, air, manufacturing, polluting