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 sense is used to determine an object's texture? (A) hearing (B) smell (C) taste (D) touch?
Example Output: sense, determine, texture?

Example Input: Question: Charisma has a goldfish she keeps in a tank. She planted several underwater plants in the bottom of the tank. How are the goldfish and the plants in the tank similar? (A) Both add oxygen to the water. (B) Both perform photosynthesis. (C) Both are made up of cells. (D) Both eat food.?
Example Output: goldfish, plants, tank, similar?

Example Input: Question: Mark determined that a softball travels a greater distance than a basketball when thrown with the same amount of force. What is the variable in this experiment? (A) Person throwing the ball (B) Type of ball (C) Amount of force (D) Humidity of the air?
Example Output:
softball, distance, basketball, amount, force., variable