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.

Question: Why is it winter in North America when it is summer in South America?
winter, North, America, summer, South, America?

Question: Which of the following limited resources are desert shrubs and seed-harvester ants MOST likely to compete over in the Mojave Desert? (A) rainwater from the occasional storm (B) sand to make a suitable shelter (C) oxygen from the desert air (D) a mate for reproduction?
limited, resources, desert, shrubs, ants, compete, Mojave, Desert?

Question: Jessica watches the Sun set in the evening sky. What causes the setting of the Sun? (A) The distance between Earth and the Sun is increasing. (B) The tilt of Earth on its axis is constantly changing. (C) Earth is revolving around the Sun. (D) Earth is rotating on its axis.?

Sun, set, causes, setting, Sun?