Answer: Cloud Functions

**C is correct** because Cloud Functions is a serverless compute platform that charges based on invocations and CPU time, scaling down to zero when there is no traffic. This makes it ideal for applications with intermittent usage, such as those only accessed during business hours, as it minimizes costs by not charging when the application is idle. **A is incorrect** because Compute Engine requires a VM to be active continuously, incurring costs even during idle periods, making it less cost-effective for this scenario. **B is incorrect** because Google Kubernetes Engine (GKE) does not automatically scale down to zero. The underlying nodes and clusters continue to incur costs regardless of application activity. **D is incorrect** because App Engine flexible environment requires instances to remain active, leading to unnecessary costs during idle times. For more details on pricing and scaling, visit [Google Cloud Functions Pricing](https://cloud.google.com/functions/pricing).

Author: LeetQuiz Editorial Team