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 electrical energy that is generated at a power plant travels through wires to houses and businesses. Not all of the energy that is generated arrives at its destination, why is this? (A) Some of the electrical energy is converted into motion in the wires. (B) Some of the electrical energy is converted into heat in the wires. (C) Some of the electrical energy is converted into light in the wires. (D) Not all of the electrical energy can travel in the wires.?
Example Output: electrical, energy, power, plant, wires, houses, businesses., energy

Example Input: Question: A student in an empty classroom shouts, "Hello!" Which best explains what the student hears after the shout? (A) an increased loudness of sound (B) a reflection of sound (C) an increased frequency of sound (D) a refraction of sound?
Example Output: explains, hears, shout?

Example Input: Question: What is a waste product excreted by lungs? (A) Oxygen (B) Carbon dioxide (C) Mucous (D) Sweat?
Example Output:
waste, excreted, lungs?