Option D uses fewest number of steps.

Be careful. The question states "each IP address that accesses the API". VPC Flow Logs is sampling records: "VPC Flow Logs records a sample of network flows sent from and received by VM instances, including instances used as GKE nodes. These logs can be used for network monitoring, forensics, real-time security analysis, and expense optimization." Source: https://cloud.google.com/vpc/docs/using-flow-logs C. Is the correct answer.

Choose option D. To configure Cloud Logging to log each IP address accessing the API with the fewest steps in a Compute Engine environment using an internal TCP/UDP load balancer, the first step would be to enable VPC Flow Logs on the subnet. That will allows you to capture network flow information, including source and destination IP addresses, as traffic passes through the load balancer. VPC Flow Logs provide detailed visibility into network activity without requiring modifications to individual instances or the installation of additional agents. Enabling VPC Flow Logs is a straightforward and efficient way to capture the necessary information for logging IP addresses accessing the API in a Compute Engine environment.

D. Enable VPC Flow Logs on the subnet. This will capture the network traffic details you need for logging in Cloud Logging without requiring additional configurations on the instances or firewall rules.