Answer:
One reason sub-plots which are used in novels is to develop the novel’s theme in more depth. So, here the right answer would be Option B.
Step-by-step explanation:
A subplot is always in parallel with the main plot. The main plot narrates a chain of incidents, introduces the characters and their reaction to different situations throughout the story. The subplot works behind-the-scenes. It shows the impulses that lead a character to react in a particular way thus, giving it more matter to develop.
It fills in the gaps left by the main plot to give a storyline a complete look. It gives birth to the theme and the tone of the storyline which help the readers to understand why a particular situation or incident took place and what effect it had on the characters and what was the outcome of it.