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: What part of a woolly mammoth is least likely to be found as a fossil? (A) Teeth (B) Skull (C) Muscle (D) Tusks?
Example Output: part, woolly, mammoth, least, likely, fossil?

Example Input: Question: Which of the following is the best observation of the refraction of light? (A) Looking at oneself in a mirror (B) Looking at a shadow of an object (C) Viewing an object through an open window (D) Viewing an object partially in water?
Example Output: observation, refraction, light?

Example Input: Question: A pot is heated on a stove. Which process causes the metal handle of the pot to also become hot? (A) combustion (B) convection (C) radiation (D) conduction?
Example Output:
pot, stove., process, causes, metal, handle, become, hot?