Which of the following commands changes the ownership of file.txt to the user dan and the group staff?

A forward slash is not a valid delimiter in chown syntax; only the colon character separates the user from the group name.

The standard chown syntax for simultaneously setting both owner and group is chown user:group file, where a colon delimiter separates the two values. Running chown dan:staff file.txt sets the owning user to dan and the owning group to staff exactly as required.

chown does not recognize -u or -g flags; those option letters belong to other utilities such as id or install, and passing them to chown results in an error.

chown does not support a -g flag in any form; mixing a positional username argument with this unsupported flag produces a syntax error.