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: What tool is used to determine the mass of an object? (A) Balance (B) Meter stick (C) Thermometer (D) Graduated cylinder?

Ex Output:
tool, determine, mass


Ex Input:
Question: Which would cause the most soil to erode from a river bank in just a few days? (A) animals climbing up the river bank (B) acid rain falling onto the river bank (C) heat from the sun drying the river bank (D) water from a flood flowing over the river bank?

Ex Output:
soil, erode, river, bank, days?


Ex Input:
Question: Ice wedging is __________. (A) a term used in rock and ice climbing (B) the freezing and thawing of water in rock cracks (C) the process that forms glaciers (D) the crystallization of freezing water to form snow flakes?

Ex Output:

Ice, wedging