Explanation
The correct command to change the ownership of file.txt to the user dan and the group staff is chown dan:staff file.txt. This command uses the colon (:) as a separator between the user and the group. The other options are incorrect because they use the wrong syntax or options for the chown command.Option A uses a slash (/) instead of a colon, which is not valid. Option C uses the -u and -g options, which are not supported by the chown command. Option D uses the -g option, which only changes the group, not the user. References:
* [LPI Linux Essentials - 1.3 Basic File Management]
* [LPI Linux Essentials - 2.1 Using Devices, Linux Filesystems, Filesystem Hierarchy Standard]
* [LPI Linux Essentials - 2.2 Mounting, Unmounting Filesystems]
* [LPI Linux Essentials - 2.3 Disk Partitions]
* Chown Command in Linux: How to Change File Ownership - phoenixNAP
* chown command in Linux with Examples - GeeksforGeeks
* Chown Command in Linux: How to Use It - Help Desk Geek
* Chown Command in Linux (File Ownership) | Linuxize