The correct answer is "grammar"
Linguist is a person who studies languages, semantics is the science of word and sentence meaning, and arbitrary means that something is subjected to individual will or judgement.
Explanation:
Harry Bittering and his family are among the first thousand Earthmen to move to Mars for the purpose of colonizing it. Yet Bittering feels out of place in his new home. His uneasiness is so profound that he wants his family to return with him to Earth. He has decided that Mars is meant to be inhabited only by Martians.
It's the problem or problems in the story.
