Science fiction has been described as the genre that, by addressing the future, that it concerns ideas of large scope rather than the ephemeral thoughts and emotions of individuals.
Preposition phrase - "by addressing the future" modifies "Science fiction has been described as the genre"
that clause also describes "the genre" - so we can't have two that in the same sentence - A and B are out.
D. so concerns ideas of large scope instead of the ephemeral thinking
that so concerns ideas of .... is incorrect
E. it concerns ideas of large scope but not the ephemeral thoughts
it refers to genre - the structure is - ....as the genre that genre concerns ideas..... - Incorrect
Option C
Science fiction has been described as the genre that, by addressing the future, concerns ideas of large scope rather than the ephemeral thoughts and emotions of individuals.
Correct. C is clear in meaning and concise.
Answer C