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.

Example Input: Question: Which activity is an example of a chemical change? (1) dissolving table salt in water (2) hammering aluminum into thin sheets (3) melting gold to make jewelry (4) burning wood to produce ashes?
Example Output: example, chemical, change?

Example Input: Question: Which is an example of a decomposer? (A) a hawk (B) a mouse (C) a flower (D) a mushroom?
Example Output: example, decomposer?

Example Input: Question: Different systems of the human body perform different functions. Which system takes oxygen from the air to be moved by the circulatory system? (A) the respiratory system (B) the digestive system (C) the nervous system (D) the skeletal system?
Example Output:
systems, human, body, functions., system, takes, oxygen, air, circulatory