What command is used to mount a floppy disk image under /mnt/floppy?

`mount -loop` is syntactically incorrect; the option for loopback device is `-o loop`.

`mount root.img /mnt/floppy` would attempt to mount the file `root.img` directly, which requires it to be a block device, not just a regular file.

C is correct because the `-o loop` option is essential when mounting a file (like `root.img`) as a block device. This allows the `mount` command to interpret the image file as a filesystem that can then be mounted at the specified mount point `/mnt/floppy`.

`mount root.img` is incomplete and doesn't specify a mount point.

`mount -l` is not a standard option for loopback mounting; `-l` typically means "label".