TASK DEFINITION: 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.
PROBLEM: 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?

SOLUTION: explains, hears, shout?

PROBLEM: Question: Sally is making candy on the stove. She places a thermometer in the candy. What is she measuring? (A) length (B) speed (C) temperature (D) weight?

SOLUTION: thermometer, measuring?

PROBLEM: Question: When a butterfly emerges from its chrysalis, its wings are crumpled. In order to expand its wings, the butterfly hangs upside down, causing fluid to be pumped into the veins of its wings. This pumping most likely expands the wings by — A increasing the pressure inside the wings B decreasing the density of the wings C increasing the temperature inside the wings D decreasing the mass of the wings?

SOLUTION:
butterfly, hangs, upside, fluid, pumped, veins, pumping, expands