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.

[Q]: Question: Helen combined yellow sulfur and black iron filings together. What is the easiest way for her to separate this mixture? (A) They cannot be separated because they are chemically combined. (B) She can put the mixture in water and wait for the iron filings to rust. (C) They cannot be separated because they are physically combined. (D) She can use a magnet to attract the iron filings from the mixture.?
[A]: yellow, sulfur, iron, filings, separate, mixture?


[Q]: Question: What effect does a producer have on the food chain? (A) It makes energy for the food chain. (B) It recycles material in the food chain. (C) It eats food in the food chain. (D) It stops the food chain from working.?
[A]: effect, producer, food, chain?


[Q]: Question: Which land form is the result of the constructive force of a glacier? (A) valleys carved by a moving glacier (B) piles of rocks deposited by a melting glacier (C) grooves created in a granite surface by a glacier (D) bedrock hills roughened by the passing of a glacier?
[A]:
land, form, result, constructive, force, glacier?