The correct answer is B. Modify the network ACL that is associated with the CIDR range to allow outbound traffic to ephemeral ports.

This answer is correct because network ACLs are stateless, which means that they do not automatically allow return traffic for inbound connections. Therefore, the network ACL that is associated with the CIDR range of the new application must have outbound rules that allow traffic to ephemeral ports, which are the temporary ports used by the vendors’ machines to communicate with the application servers.Ephemeral ports are typically in the range of 1024-655351. If the network ACL does not have such rules, the vendors will not be able to connect to the application.

The other options are incorrect because:

A. Modifying the security group that is associated with the EC2 instances to have the same outbound rules as inbound rules is not a solution, because security groups are stateful, which means that they automatically allow return traffic for inbound connections.Therefore, there is no need to add outbound rules to the security group for the vendors to access the application2.

C. Modifying the inbound rules on the internet gateway to allow the required ports is not a solution, because internet gateways do not have inbound or outbound rules. Internet gateways are VPC components that enable communication between instances in a VPC and the internet.They do not filter traffic based on ports or protocols3.

D. Modifying the network ACL that is associated with the CIDR range to have the same outbound rules as inbound rules is not a solution, because it does not address the issue of ephemeral ports.The outbound rules of the network ACL must matchthe ephemeral port range of the vendors’ machines, not necessarily the inbound rules of the network ACL4.