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 Q]: Question: In the life cycle of a fly, which stage comes after the larval stage? (A) egg (B) adult (C) nymph (D) pupa?
[EX A]: cycle, stage, larval, stage?

[EX Q]: Question: How does a human body get energy? (A) Sunlight on the skin produces energy. (B) Water provides the majority of energy. (C) Food and oxygen combine to deliver energy. (D) Sleep provides energy stored at night for the next day.?
[EX A]: human, body, get, energy?

[EX Q]: Question: The main function of the human digestive system is to (1) break down foods for absorption into the blood (2) exchange oxygen and carbon dioxide in the lungs (3) release energy from sugars within the cells (4) carry nutrients to all parts of the body?
[EX A]:
function, digestive, system