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

This syntax is incorrect as `setfattr` requires `-n` for the attribute name and `-v` for the value.

The `setfattr` command uses the `-n` (or `n`) option to specify the attribute name and the `-v` (or `v`) option to specify its value. The format `setfattr n user.author v "A. Author" afile.txt` correctly applies the attribute `user.author` with the value "A. Author" to `afile.txt`.

This syntax is incorrect for `setfattr`; it expects separate options for the attribute name and value.

The `-a` option is for appending to the end of a value, which is generally not supported for attributes like this, and the command is still missing the `-n` and `-v` flags required for setting an attribute value.