The correct answer is letter A. Theme is the central message or insight into life revealed by a literary work. Oxford English Dictionary even defined the word theme as “the central topic a text treat.” There are different sorts of themes that an author can combine to convey his or her message, but generally themes can be either major or minor.
If an author wants to write about compassion, as shown in the 1877 novel by Anna Sewell entitled Black Beauty, she needed to write a story wherein it revolves around that specific theme. However, it does not necessarily mean that she can limit her story with just that certain theme. She also wrote about love in the book which we can consider as a minor theme, but such minor theme added to the whole story of the novel.