Your company wants you to build a highly reliable web application with a few public APIs as the backend. You don't expect a lot of user traffic, but traffic could spike occasionally. You want to leverage Cloud Load Balancing, and the solution must be cost-effective for users. What should you do?

The correct answer leverages serverless services, which are ideal for cost-effectiveness with infrequent or spiky traffic. Cloud Storage is a highly available and cost-effective solution for static content. Cloud Functions provides a fully managed, pay-per-execution environment for APIs, scaling automatically from zero to handle spikes without incurring costs when idle. Firestore is a serverless NoSQL database that scales automatically and is cost-effective for variable usage patterns. Storing static content in Cloud CDN (option 1 and 3) is good for performance but adds cost for a low-traffic application. App Engine (option 1) can be cost-effective but might be overkill for "a few public APIs." Google Kubernetes Engine (option 2) is generally more complex and expensive to manage for a low-traffic application, even with zonal redundancy. Cloud Spanner (option 2) is a highly scalable relational database, but its cost might be excessive for an application not expecting high traffic. Cloud Run (option 3) is a good serverless option, but Cloud Functions is even more granular for simple APIs.