The team requires a manual approval action before the application is deployed, even if the test is successful." So the approval action is before the deployment not the tests. Answer B is the right one here.

Explanation
The AWS documentation mentions the following
Amazon RDS Read Replicas provide enhanced performance and durability for database (DB) instances. This replication feature makes it easy to elastically scale out beyond the capacity constraints of a single DB Instance for read-heavy database workloads. You can create one or more replicas of a given source DB Instance and serve high-volume application read traffic from multiple copies of your data, thereby increasing aggregate read throughput. Read replicas can also be promoted when needed to become standalone DB instances.
For more information on AWS RDS Read Replica's, please visit the below URL:
https://aws.amazon.com/rds/details/read-replicas/
Amazon OastiCache is a web service that makes it easy to deploy, operate, and scale an in-memory data store or cache in the cloud. The service improves the performance of web applications by allowing you to retrieve information from fast, managed, in-memory data stores, instead of relying entirely on slower disk-based databases.
For more information on AWS Clastic Cache, please visit the below URL:
* https://aws.amazon.com/elasticache/

In DynamoDB, a secondary index is a data structure that contains a subset of attributes from a table, along with an alternate key to support Query operations.

Explanation
As your infrastructure grows, common patterns can emerge in which you declare the same components in each of your templates. You can separate out these common components and create dedicated templates for them.
That way, you can mix and match different templates but use nested stacks to create a single, unified stack.
Nested stacks are stacks that create other stacks. To create nested stacks, use the AWS:: Cloud Form ation::Stackresource in your template to reference other templates. For more information on Cloudformation best practises please refer to the below link:
* http://docs.aws.amazon.com/AWSCIoudFormation/latest/UserGuide/best-practices.html