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 represents a chemical reaction? (A) a sugar cube dissolving in water. (B) ice cubes forming in a freezer. (C) ice cream melting in a bowl. (D) a cake baking in an oven.?
[A]: chemical, reaction?


[Q]: Question: Based on analysis of deep ice cores from the Arctic, scientists theorize that early humans caused air pollution. These scientists can make sure their data is correct by (A) analyzing only melted ice cores. (B) analyzing more than one ice core. (C) comparing their data to the expected results. (D) comparing their data to modern pollution levels.?
[A]: theorize, humans, caused, air, pollution., data, correct


[Q]: Question: A group of fifth grade students go to the school park on a sunny day and measure the length of their shadows at 10:00 AM, at noon, and at 2:45 PM. To measure and record the data from their observations, they use a ___. (A) thermometer and balance (B) clock and measuring tape (C) clock and calculator (D) clock and thermometer?
[A]:
measure, length, shadows, 10:00, 2:45, PM., use