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: A metric ruler can be used to measure the ____ (A) volume of a liquid. (B) circumference of a circle. (C) length of a stick. (D) curve of an oval.?
[A]: metric, ruler, measure


[Q]: Question: What causes nighttime and daytime on Earth? (A) the Sun rotating on its axis (B) Earth rotating on its axis (C) Earth revolving around the Sun (D) the Moon revolving around Earth?
[A]: causes, nighttime, daytime, Earth?


[Q]: Question: Which one of the following statements best explains why we use simple machines? (A) A simple machine can change the direction or amount of force to make work easier. (B) A simple machine can change the amount of Earth's gravity acting on an object to make it lighter. (C) A simple machine can change the magnetic attraction and repulsion of an object to create energy. (D) All of the answers are correct.?
[A]:
explains, use, simple, machines?