The correct answer is D because family names are attributes of images, not instances. The gcloud compute images list command is used to list all images available in a project, including their family names. This is essential for managing images, as image families group related images together, simplifying version management. For example, the debian-9 family in the debian-cloud project always points to the latest Debian 9 image. Options A, B, and C are incorrect as they either list instances or incorrectly attempt to show families for instances, which does not apply here.