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: A student walks across a carpeted floor. When she touches a doorknob she sees a spark and feels a shock. Which force is responsible for the spark and shock? (A) Electrical (B) Friction (C) Gravitational (D) Magnetic?
Example Output: walks, carpeted, floor., touches, doorknob, sees, spark, shock., force

Example Input: Question: A seed of a plant sticks to the fur of an animal as it walks by. How has the animal most likely helped the plant? (A) by spreading the seed (B) by sprouting the plant (C) by scattering the pollen (D) by fertilizing the ground?
Example Output: seed, plant, sticks, fur, animal, animal, helped, plant?

Example Input: Question: The primary force responsible for MOST of the transportation of pebbles, sand, silt and mud is __________. (A) deposition (B) wind (C) moving water (D) glaciers?
Example Output:
primary, force, responsible, transportation, silt, mud