Correct answer: C. This option combines the most effective strategies for each service. Autoscaling and managed instance groups optimize Compute Engine resource utilization, object lifecycle policies help manage Cloud Storage costs, automatic storage increase in Cloud SQL ensures optimal storage usage, and monitoring Cloud Pub/Sub usage allows for efficient quota management.

• A: Incorrect. This approach may not provide the required performance and availability for a multi-tier web application. Preemptible VMs have a limited lifespan and can be terminated at any time, which may not be suitable for production workloads. Additionally, the Always Free tier has limitations that might not meet the application requirements.
• B: Incorrect. The GCP Cost Calculator can provide cost estimates, but it does not optimize resource utilization by itself. Using a custom machine type for each instance may not provide the desired cost savings, and disabling all Cloud SQL instances and Cloud Pub/Sub topics can cause the application to malfunction.
• D: Incorrect. Consolidating the entire application into a single Compute Engine instance can lead to performance bottlenecks and single points of failure. This approach may not address the cost and utilization concerns effectively.