According to official Xen xl toolstack documentation, the correct sub-commands used to change media in a virtual CD-ROM drive are cd-insert and cd-eject. These commands are specifically designed for inserting or ejecting ISO media from a Xen guest's virtual CD-ROM device.

While commands such as block-attach and block-detach are valid xl sub-commands, they are used for attaching and detaching block devices in general and are not specific to CD-ROM media operations. The provided solution lists multiple commands, including incorrect and unrelated ones, rather than specifying the correct sub-command precisely.

Because the solution does not accurately and exclusively identify the correct xl sub-command, it is considered incorrect. Therefore, the correct determination is B.