A user reports that they cannot write to a file named 'report.txt' which should be writable by members of the group 'staff'. As a sysadmin, you check the permissions with ls -l report.txt and the output shows -rw-r--r-- 1 root staff 1048576 Jan 01 12:34 report.txt. What is the most likely reason for the user being unable to write to the file?
The group 'staff' does not exist on the system
The file is too large to be written to by group members
The file is owned by the 'root' user, so only root can modify it
The file only has write permissions for the owner