Final answer:
A serial structure (d) is an open-ended approach to storytelling that is commonly used in serialized forms such as television series.
Step-by-step explanation:
The structure that replaces a traditional plot with an open-ended serial structure is the serial structure (d). Unlike linear or casual plots that move chronologically, the serial structure of storytelling allows for a series of episodic events that do not necessarily follow a fixed sequence and can continue over multiple episodes or installments. This type of structure is common in television series and other forms of serialized storytelling.
In a serial structure, the focus is on character development and overarching themes rather than a singular, conclusive plot. Each episode or installment builds on the previous one while also setting up threads for future development, which is why this form is known for keeping the narrative open-ended. While a linear narrative adheres to a straightforward cause-effect chain, the serial structure embraces a more complex and layered approach to storytelling.