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.

[Q]: Question: Humans have bacteria inside as well as outside the body. These bacteria are __________. (A) both beneficial and harmful (B) harmful and spread disease (C) harmful all of the time (D) helpful all of the time?
[A]: Humans, bacteria, inside, outside, body.


[Q]: Question: Which of the following systems breaks food into nutrients that can be used by the body? (A) circulatory. (B) digestive. (C) respiratory. (D) reproductive.?
[A]: systems, breaks, food, nutrients, body?


[Q]: Question: A mountain with a melting glacier has a stream with a waterfall. The waterfall fills a lake at the base of the mountain. Where is the water coldest? (A) glacier (B) stream (C) waterfall (D) lake?
[A]:
mountain, melting, glacier, stream, waterfall., fills, lake, coldest?