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: A student saw a deer while on a hike in the woods. By looking at the deer, she could tell the (A) exact height of the deer (B) color of the deer (C) exact weight of the deer (D) exact temperature of the deer?
Example Output: looking, tell

Example Input: Question: The primary reason that plants are important for an ecosystem is because they (A) provide energy for consumers. (B) depend on other organisms for shelter. (C) break down dead animal matter. (D) consume nutrients for energy.?
Example Output: reason, plants, important, ecosystem

Example Input: Question: Many leaves appear green because the leaves (A) resist green light. (B) bend all colors except green. (C) reflect green light. (D) reflect all colors except green.?
Example Output:
leaves, appear, green