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: The main function of hormones in the human body is to (1) identify and destroy microbes (2) regulate body functions (3) transport blood to cells (4) store energy?
Example Output: function, hormones, body

Example Input: Question: A group of fifth grade students go to the school park on a sunny day and measure the length of their shadows at 10:00 AM, at noon, and at 2:45 PM. To measure and record the data from their observations, they use a ___. (A) thermometer and balance (B) clock and measuring tape (C) clock and calculator (D) clock and thermometer?
Example Output: measure, length, shadows, 10:00, 2:45, PM., use

Example Input: Question: Which of the following is a property of CO2 gas? (A) It feels like a rock. (B) It smells like a lemon. (C) It is colorless. (D) It is hard.?
Example Output:
property, CO2, gas?