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 Q]: Question: Plants on hills keep dirt in place during a rain storm. Plant roots grow into the dirt and keep the dirt from moving. Why do roots grow into the dirt? (A) to release gases (B) to release water (C) to absorb energy (D) to absorb nutrients?
[EX A]: roots, grow, dirt?

[EX Q]: Question: Which of the following BEST describes what happens when magnets repel each other? (A) the magnets create electricity (B) the magnets pull toward each other (C) the magnets push away from each other (D) nothing happens?
[EX A]: magnets, repel

[EX Q]: Question: A student is studying the conduction of heat through different materials. He places each of three identically-sized blocks of rubber, copper, and wood on three different hot plates. On top of each block, he places a 2-gram piece of ice and then turns each hot plate on to warm. Based on the given scenario, what variable would the student measure to determine which material is the best conductor of heat? (A) Density of each material (B) Temperature of each material when the ice begins to melt (C) Time required for the ice to completely melt (D) Temperature of each hot plate?
[EX A]:
conduction, heat, materials., identically-sized, blocks, wood, hot, plates., top, piece, ice, hot, plate, variable, measure, determine, material, conductor, of