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 we eat pizza, it is digested by the body to provide us energy. This is an example of extracting which kind of energy? (A) chemical (B) light (C) heat (D) kinetic?
Example Output: eat, digested, energy., example, extracting, energy?

Example Input: Question: Which pair of English and metric units has most nearly the same value? (A) liter and quart (B) gram and ounce (C) kilogram and pound (D) kilometer and mile?
Example Output: English, metric, units, value?

Example Input: Question: Corals are animals that live in tropical oceans. Fossils of corals are found in Ohio. What does the presence of coral fossils suggest about how the environment of Ohio has changed over time? (A) Ohio was once covered by warm seas. (B) A large glacier once passed over Ohio. (C) The average rainfall in Ohio is now much more than it once was. (D) The average temperature in Ohio is now much warmer than it.?
Example Output:
corals, Ohio., coral, fossils, suggest, environment, Ohio, changed