Your team is using the AWS CodeBuild service for an application build. As part of Integration testing during the build phase, the application needs to access an RDS instance in a private subnet. How can you ensure that this is possible?

Answer options:

A.Create a NAT Endpoint and ensure the codebuild project configuration is modified with the endpoint information.
B.Provide additional VPC-specific configuration information as part of your AWS CodeBuild project.
C.Mark the subnet as a public subnet during the time of the Integration tests.
D.Use a NAT gateway to relay the requests from AWS CodeBuild to the RDS Instance.

Answer - B
This is given in the AWS Documentation.
Typically, resources in a VPC are not accessible by AWS CodeBuild. To enable access, you must provide additional VPC-specific configuration information as part of your AWS CodeBuild project configuration. This includes the VPC ID, the VPC subnet IDs, and the VPC security group IDs. VPC-enabled builds are then able to access resources inside your VPC. 
VPC connectivity from AWS CodeBuild builds makes it possible to:
Run integration tests from your build against data in an Amazon RDS database that`s isolated on a private subnet.
Query data in an Amazon ElastiCache cluster directly from tests.
Interact with internal web services hosted on Amazon EC2, Amazon ECS, or services that use internal Elastic Load Balancing.
Since the requirements are clearly mentioned in the documentation, all other options are incorrect.
For more information on VPC support for AWS CodeBuild, please refer to the below URL-
https://docs.aws.amazon.com/codebuild/latest/userguide/vpc-support.html