Answer :
Cambridge English Dictionary defines "theme" as "A theme is also the main idea of a work of literature or art."
Cambridge English Dictionary defines "moral" as "The moral of a story, event, or experience is the message that you understand from it about how you should or should not behave."
According to the above definitions, for stories that have a moral, the following statement about the theme is true :
b) The theme is the central message revealed through the story.