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 sequence represents the order of development for many plants? (1) seed develops inside fruit -> seed is dispersed -> seed germinates -> plant grows (2) seed is dispersed -> seed develops inside fruit -> seed germinates -> plant grows (3) seed germinates -> plant grows -> seed is dispersed -> seed develops inside fruit (4) seed is dispersed -> plant grows -> seed germinates -> seed develops inside fruit?
Example Output: order, development, plants?

Example Input: Question: The interaction of the skeletal and muscular systems to produce locomotion is coordinated by which human body system? (1) circulatory (2) excretory (3) nervous (4) respiratory?
Example Output: interaction, skeletal, muscular, locomotion, coordinated, system?

Example Input: Question: Animals eat plants or other animals. How much and what they eat affects other parts of the ecosystem. These interrelationships between the living things in an ecosystem is called ___. (A) interdependence (B) decomposition (C) environment (D) food webbing?
Example Output:
interrelationships, living, things, ecosystem