Which feature must an administrator use to revert to a previous version of a VM template?

An administrator must use the Content Library feature to revert to a previous version of a VM template because it provides a mechanism for managing and storing VM templates and other content centrally. The Content Library allows for the creation of versioned templates, meaning that once a VM template is updated or modified, the previous versions can still be accessible. This is particularly useful for maintaining different configurations or setups without losing the older versions of the template.

In contrast, VM Snapshots are primarily used for creating point-in-time copies of a virtual machine's current state, allowing for restoration of the VM to that exact state rather than specifically managing template versions. Storage vMotion is a feature used for migrating virtual machine disk files across different storage devices without downtime, and it does not relate to template version management. VMware Tools is a suite of utilities that enhances the performance of the VM and improves management but does not serve the function of reverting or managing version history of templates.

Hence, using the Content Library provides the right framework for successful template version control and rollbacks.