A Shared VPC Admin can define a Security Admin by granting an IAM member the Security Admin (compute.securityAdmin) role to the host project. Security Admins manage firewall rules and SSL certificates.

The correct answer is C. Create a single Shared VPC and attach each Google Cloud project as a service project.
This answer is based on the following facts:
A Shared VPC allows you to share one or more VPC networks across multiple Google Cloud projects1. This simplifies the deployment and management of the network infrastructure, as you only need to create and maintain one VPC network for all your internal projects.
A Shared VPC consists of a host project that owns the VPC network and one or more service projects that use the VPC network2. You can attach and detach service projects as needed, depending on the lifecycle of your internal projects. You can also delete service projects without affecting the host project or other service projects.
A Shared VPC allows you to delegate administrative roles to different project owners3. You can grant the Shared VPC Admin role to the owner of the host project, who can manage the VPC network and its subnets. You can also grant the Service Project Admin role to the owners of the service projects, who can manage the Google Cloud resources in their own projects.
The other options are not correct because:
Option A is not suitable. Creating a single project and additional VPCs for each internal project will increase the complexity and cost of the network infrastructure. You will need to create and maintain multiple VPC networks, firewall rules, routes, and VPN tunnels. You will also have a limit on the number of VPC networks per project4.
Option B is not feasible. Creating a single project and single VPC for each internal project will not meet the requirement of having separate project owners for each internal project. You will have only one project owner who can manage all the Google Cloud resources in the same project.
Option D is not optimal. Creating a Shared VPC and service project for each internal project will not meet the requirement of having a simple and reusable code with centralized management. You will need to create and maintain multiple Shared VPCs, which will increase the complexity and cost of the network infrastructure. You will also have more Terraform code to write and manage for each Shared VPC.

https://cloud.google.com/security/encryption-in-transit/ Automatic encryption between GFEs and backends For the following load balancer types, Google automatically encrypts traffic between Google Front Ends (GFEs) and your backends that reside within Google Cloud VPC networks: HTTP(S) Load Balancing TCP Proxy Load Balancing SSL Proxy Load Balancing