Can someone please provide explanation why options "B" & "C" are the correct options?

Generally, for building a hierarchical relationship model, a graph database such as Amazon Neptune is a better choice. In some cases, however, DynamoDB is a better choice for hierarchical data modeling because of its flexibility, security, performance, and scale. https://docs.aws.amazon.com/prescriptive-guidance/latest/dynamodb-hierarchical-data-model/introduction.html

1. Low latency - DynamoDB is a fully managed NoSQL database service that provides fast and predictable performance with single-digit millisecond latency. Redshift is a data warehouse solution optimized for complex analytical queries, so query latency would typically be higher. Since the requirements specify minimum latency for high-traffic queries, DynamoDB is better suited. 2. Scalability - DynamoDB is highly scalable, able to handle very high read and write throughput with no downtime. Redshift also scales, but may experience some downtime during rescale operations. For a high-traffic application, DynamoDB's scalability and availability are better matched.

3. Hierarchical data - DynamoDB supports hierarchical (nested) data structures well in a NoSQL data model. Defining hierarchical employee data may be more complex in Redshift's columnar SQL data warehouse structure. DynamoDB is built around flexible data schemas that can represent complex relationships. 4. Data export - Both DynamoDB and Redshift allow exporting data to S3, so that requirement could be met with either service. However, overall DynamoDB is the better fit based on the points above regarding latency, scalability, and support for hierarchical data.