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: One important difference between living things and nonliving things is that only living things have (1) compounds (2) elements (3) molecules (4) cells?
Example Output: difference, living, nonliving, things, living

Example Input: Question: Which two observations are both used to describe weather? (A) precipitation and runoff (B) temperature and sky conditions (C) wind speed and erosion (D) types of clouds and deposition?
Example Output: observations, describe, weather?

Example Input: Question: Which characteristic do single-celled organisms and multicellular organisms have in common? (A) Both have cells with specialized functions for each life process. (B) Both perform all life processes within one cell. (C) Both have a way to get rid of waste materials. (D) Both are able to make food from sunlight.?
Example Output:
characteristic, single-celled, multicellular, organisms, common?