How should you design this topology?

Your end users are located in close proximity to us-east1 and europe-west1. Their workloads need to communicate with each other. You want to minimize cost and increase network efficiency.

How should you design this topology?
A . Create 2 VPCs, each with their own regions and individual subnets. Create 2 VPN gateways to establish connectivity between these regions.
B . Create 2 VPCs, each with their own region and individual subnets. Use external IP addresses on the instances to establish connectivity between these regions.
C . Create 1 VPC with 2 regional subnets. Create a global load balancer to establish connectivity between the regions.
D . Create 1 VPC with 2 regional subnets. Deploy workloads in these subnets and have them communicate using private RFC1918 IP addresses.

Answer: D

Explanation:

https://cloud.google.com/vpc/docs/using-vpc#create-auto-network

We create one VPC network in auto mode that creates one subnet in each Google Cloud region automatically. So, region us-east1 and europe-west1 are in the same network and they can communicate using their internal IP address even though they are in different Regions. They take advantage of Google’s global fiber network.