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: Which of the following is the best observation of the refraction of light? (A) Looking at oneself in a mirror (B) Looking at a shadow of an object (C) Viewing an object through an open window (D) Viewing an object partially in water?
[A]: observation, refraction, light?


[Q]: Question: Paul is waiting for the traffic light to change so he can cross the street. What form of energy is present in Paul as he waits to cross the street? (A) Mechanical (B) Muscular (C) Potential (D) Kinetic?
[A]: waiting, form, energy, present


[Q]: Question: Which of the following would help reduce the need for competition? (A) Large amounts of space, food, and water (B) Reduced sunlight available for photosynthesis (C) Fewer healthy organisms to reproduce with (D) A long drought?
[A]:
reduce, need, competition?