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 Input:
Question: Which of the following is an example of a chemical change? (A) Boiling an egg (B) Laying an egg (C) Breaking an egg (D) Hatching an egg?

Ex Output:
example, chemical, change?


Ex Input:
Question: Which will most likely cause a decrease in predator populations? (A) an increase in prey populations (B) a decrease in prey populations (C) a decrease in decomposers (D) an increase in producers?

Ex Output:
cause, decrease, predator, populations?


Ex Input:
Question: In which example could a thermometer be used to show that heat energy is being transferred? (A) A piano is played by striking the keys. (B) A shovel is used to move dirt from one place to another. (C) A ball is thrown into the air. (D) A stove is used to boil water in a pan.?

Ex Output:

example, thermometer, show, heat, energy, transferred?