Which themes distinguish literature written in the realist era from earlier literature?
everyday life and common subjects
tragedy and extreme circumstances
unusual and terrifying themes
adventurous and fantastical episode

the theme would be A. . everyday life and common subjects 

Artists and writers during realist era love to create something that represent a certain situation truthfully, without adding any false/extreme narrative to attract attention or any supernatural element. 

So, most of their works revolves around everyday life and the problems that normal people experience.

lancelot said to the beautiful ellen i c u r a b u t l n (i see you are a beauty lancelot was the greatest and worst of the knights who became the king's champion and undertook quests in the king's name. he became the adulterous lover of queen guinevere, and they had a son named galahad.