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: Carbon dioxide is necessary for photosynthesis to happen. How do plants absorb carbon dioxide from the atmosphere? (A) Through the petals (B) Through the stigma (C) Through the stomata (D) Through the stem?
[A]: plants, absorb, carbon, dioxide, atmosphere?


[Q]: Question: In addition to oxygen, which gases make up the largest percentage of Earth's atmosphere? (1) hydrogen, helium, and water vapor (2) hydrogen, methane, and ozone (3) carbon dioxide, water vapor, and nitrogen (4) carbon dioxide, methane, and helium?
[A]: gases, percentage, Earth's, atmosphere?


[Q]: Question: Why is it important to repeat an experiment several times? (A) to use up all the materials (B) to give all the students the chance to participate (C) to collect more data to fit the hypothesis (D) to determine if the results are similar?
[A]:
important, repeat, experiment