Which command will set the user.author attribute on the file afile.txt?

The syntax `user.author:"A. Author"` is incorrect for `setfattr` as it does not properly separate the attribute name and value with the required options.

The `setfattr` command requires the attribute name to be specified using the `-n` or `--name` option, and the attribute value to be specified using the `-v` or `--value` option, making `setfattr -n user.author -v "A. Author" afile.txt` the correct syntax.

The syntax `user.author="A. Author"` is not a valid way to specify an attribute name and value for the `setfattr` command.

While `-a` is an option (for add), it's typically used with `-n` and `-v`, and the structure `a user.author="A. Author"` is an incorrect command syntax for setting an attribute and its value.