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 Q]: Question: A large tree was cut down with a saw. What is the best way to estimate the age of this tree? (A) measure the height of the tree (B) measure the thickness of the bark (C) count the number of rings in the trunk (D) count the branches growing from the trunk?
[EX A]: tree, cut, saw., best, estimate, age

[EX Q]: Question: Which of the following systems breaks food into nutrients that can be used by the body? (A) circulatory. (B) digestive. (C) respiratory. (D) reproductive.?
[EX A]: systems, breaks, food, nutrients, body?

[EX Q]: Question: Which form of energy is found in food? (A) chemical (B) electrical (C) sound (D) mechanical?
[EX A]:
energy, found, food?