The correct answer is D because it meets the following requirements: * It matches the hub-and-spoke model of the on-premises network, where each spoke is a separate VPC network that is connected to a central hub VPC network. * It minimizes management overhead and cost, because VPC Network Peering is a simple and low-cost way to connect VPC networks without using any external IP addresses or VPN gateways1. * It uses default networking quotas and limits, because VPC Network Peering does not consume any quota or limit for VPN tunnels, external IP addresses, or forwarding rules2. * It prevents connectivity between the spokes, because VPC Network Peering is non-transitive by default, meaning that a spoke can only communicate with the hub, not with other spokes1. To enforce this restriction, a third-party network appliance can be used as a default gateway in each spoke VPC network, which can filter out any traffic destined for other spokes3. Option A is incorrect because it does not minimize cost, as Cloud VPN charges for egress traffic and requires external IP addresses for the VPN gateways4. Option B is incorrect because it does not prevent connectivity between the spokes, as VPC Network Peering allows direct communication between peered VPC networks by default1. Option C is incorrect because it does not minimize cost or use default quotas and limits, for the same reasons as option A.
