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 form of energy is needed to change water from a liquid to a gas? (A) heat (B) mechanical (C) chemical (D) sound?

Ex Output:
energy, change, water, liquid, gas?


Ex Input:
Question: Which material is primarily a mixture of weathered rock and organic matter? (1) minerals (2) soil (3) ocean water (4) seashells?

Ex Output:
mixture, weathered, rock, organic, matter?


Ex Input:
Question: The structures found in a living cell can be compared to the parts of a factory that produces cars. Which part of the factory is most similar to the nucleus of a living cell? (1) a conveyor belt that transports materials (2) a storage bin that holds the pieces needed to assemble a car (3) the computer room that controls the assembly process (4) the generator that provides energy for the factory?

Ex Output:

factory, cars., factory, similar, nucleus, cell?