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: Which force causes a marble to sink to the bottom of a glass of water? (A) gravity (B) friction (C) magnetism (D) electricity?
[EX A]: force, marble, sink

[EX Q]: Question: A scientist finds the bones of a dinosaur. What could help the scientist determine the approximate age of the dinosaur bones?
[EX A]: bones, determine, age, dinosaur, bones?

[EX Q]: Question: A marble is dropped in a glass of water. Which force pulls the marble to the bottom of the glass? (A) electricity (B) friction (C) gravity (D) magnetism?
[EX A]:
force, pulls, bottom