instruction:
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.
question:
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.?
answer:
metric, ruler, measure


question:
Question: A layer of solid brittle rock comprises the outer 100 kilometers of Earth. This layer, which contains both the crust and the upper mantle, is called the (A) core. (B) sediment. (C) lithosphere. (D) hemisphere.?
answer:
100, kilometers, Earth., contains, crust, upper


question:
Question: A research team wanted to produce a smaller variety of German shepherd dogs. They mated the smallest dogs from different litters for several generations. This is an example of which concept? (1) extinction (2) mutation (3) selective breeding (4) natural selection?
answer:

German, shepherd, dogs., mated, smallest, dogs, generations., example