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.

Example Input: Question: Which statement best explains why the Sun and the Moon appear to be about the same size in the sky? (1) The Sun and the Moon have the same diameter. (2) The Moon is larger in diameter and farther from Earth than the Sun. (3) The Moon is smaller in diameter and is closer to Earth than the Sun. (4) The Sun and the Moon are the same distance from Earth.?
Example Output: Sun, Moon, appear, size

Example Input: Question: Which of the following is an example of a chemical change? (A) clouds forming (B) sugar dissolving (C) water freezing (D) a candle burning?
Example Output: example, chemical, change?

Example Input: Question: What kind of energy change occurs when a battery is operating a remote control toy? (A) Heat energy is changed to light energy. (B) Light energy is changed to heat energy. (C) Potential energy is changed to kinetic energy. (D) Kinetic energy is changed to chemical energy.?
Example Output:
energy, change, battery, remote, control, toy?