Your company needs to design a database that shows how changes in (DP-900)

Correct answer: A. graph.
A graph database is the most appropriate data store for modeling the relationships between different areas of a network and how changes in one area affect the others.
In a graph database, the network can be represented as a set of nodes (representing different areas of the network) connected by edges (representing the relationships and dependencies between them). This allows you to easily model and analyze the complex, interconnected nature of a network and how changes in one part of the network impact other parts.

The other data store types are not as well-suited for this use case:
B. Key/value stores are good for simple, unstructured data, but they don't provide the relational modeling capabilities needed to represent the network topology and dependencies.
C. Document databases are good for storing semi-structured data, but they lack the inherent support for modeling relationships that a graph database provides.
D. Columnar databases are optimized for analytical workloads on large datasets, but they are not the best fit for modeling the complex, interconnected nature of a network.

Therefore, a graph database is the most appropriate choice for designing a database to analyze how changes in network traffic in one area affect other areas of the network.