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 Input:
Question: Which of the following structures is not present in animal cells? (A) cell membrane (B) cell wall (C) mitochondrion (D) nucleus?

Ex Output:
structures, present, animal, cells?


Ex Input:
Question: Sandra puts some pill bugs into an open box. She covers half the box with a piece of cardboard. She then places the box outside on a summer day, and all the pill bugs move under the cardboard. The pill bugs are most likely responding to which of the following? (A) air pressure (B) bright light (C) wind (D) fog?

Ex Output:
open, box., outside, summer, bugs, cardboard., pill, bugs, responding


Ex Input:
Question: Rubbing sandpaper on a piece of wood produces what two types of energy? (A) heat and light (B) sound and heat (C) light and electricity (D) electricity and sound?

Ex Output:

Rubbing, sandpaper, wood, produces, energy?