Answer:
D. The author wants to add more depth and substance to the characters and story
Explanation:
Subplot adds up to the realism and depth of the story which is told. It can show us another aspect of the characters and how they act in different situations. If the primary story plot is, for example, a thriller, the romantic subplot can explain to us how characters act in emotional situations and the states of vulnerability.
The subplots add substance to the story. They can reveal many important details and can be of great value to the entertainment quality of the piece. It can also create a three-dimensionality of the secondary characters and it adds up to the twists in the main plot.
