B is correct because Deployment Manager is Google Cloud's Infrastructure as Code tool, designed for dynamically provisioning VMs on Compute Engine in a declarative format using YAML or Python templates. It aligns with Google's best practices by offering a consistent, reproducible, and automated way to manage infrastructure.

• A is incorrect as Cloud Composer is a workflow automation tool, not suited for VM provisioning.
• C is incorrect because Unmanaged Instance Groups lack dynamic provisioning capabilities and don't follow Google's best practices for this scenario.
• D is incorrect since Managed Instance Groups are for managing similar VMs in scalable pools, not for provisioning VMs with varied configurations from a file.

For more details, visit Deployment Manager and Cloud Composer.