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: When can producers make the most food? (A) summer, because there is more sunlight (B) summer, because there is more heat (C) spring, because there is more rain (D) spring, because there are more leaves?
Example Output: producers, make, food?

Example Input: Question: Like animals, plants also sense and respond to their environment. An example of this is ___. (A) growing toward the sunlight (B) climbing a trellis in the garden (C) closing its flowers at night (D) All of the answers are correct?
Example Output: plants, sense, respond, environment., example

Example Input: 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.?
Example Output:
water, renewable, resource?