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 Input:
Question: About how much of Earth's surface is covered by oceans? (A) less than 20% (B) about 50% (C) about 70% (D) more than 90%?

Ex Output:
Earth's, surface, covered, oceans?


Ex Input:
Question: After testing the ability of aluminum, wood, and plastic to conduct electricity, a student would conclude that ___. (A) aluminum is a good conductor (B) wood and plastic are good conductors (C) aluminum is a good insulator (D) wood is a good conductor?

Ex Output:
testing, plastic, conduct


Ex Input:
Question: Which object helps people understand what makes up white light? (A) Barometer (B) Prism (C) Microscope (D) Thermometer?

Ex Output:

object, understand, white, light?