A. App Engine.
Explanation:
Why A is correct:
App Engine: Google App Engine is a fully managed platform-as-a-service (PaaS) that allows developers to build and deploy applications quickly and easily without worrying about managing the underlying infrastructure. It supports continuous integration and continuous deployment (CI/CD) processes, enabling developers to stage new versions of applications easily.
Staging and Promotion: App Engine has built-in support for traffic splitting and versioning, which allows you to stage new versions of your application and gradually promote them to production. This can be done with minimal operational overhead, making it ideal for scenarios where operational functions are outsourced.
Minimal Operational Overhead: Since App Engine is fully managed, it reduces the operational burden significantly, making it easier for the outsourced operations team to handle promotions and manage the application.