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: Which of the following is the BEST example of something that causes large rocks to break into smaller rocks? (A) roots of plants (B) worms (C) wind (D) animal migration?
answer:
example, causes, large, rocks, break, smaller, rocks?


question:
Question: Why is water considered to be a renewable resource? (A) Water can be used over again. (B) Water can be found all over Earth. (C) Water can dissolve other substances. (D) Water is needed by organisms to stay alive.?
answer:
water, renewable, resource?


question:
Question: An object travels slowly over a bumpy surface and fast over a smooth surface. The difference is due to (A) mass. (B) friction. (C) energy. (D) magnetism.?
answer:

object, travels, slowly, bumpy, fast, smooth, difference