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: Tisha visited the same beach two summers in a row. She found that some sand dunes that were there the first summer were gone the next summer. Farther down the beach she saw many more sand dunes that had not been there before. What most likely caused this change? (A) Wind blew the sand and deposited it elsewhere. (B) Waves deposited shells and seaweed on the beach. (C) The salt from the ocean settled out of the water onto the beach. (D) The Sun's energy warmed the sand, causing it to expand.?
Example Output: beach, two, summers, row., sand, dunes, summer, gone, beach, sand, dunes, caused, change?

Example Input: Question: A scientist wanting to document a change in a river's flow pattern should observe a river over a period of (A) days. (B) weeks. (C) months. (D) years.?
Example Output: change, river's, flow, pattern, observe, period

Example Input: Question: Oscar is investigating how many days it takes for a chick to hatch from an egg. Which number of eggs would give Oscar the most reliable results? (A) 1 (B) 3 (C) 5 (D) 7?
Example Output:
days, chick, hatch, egg., number, eggs, reliable, results?

