Which of the following is correct when talking about mount points?

Any existing directory within the filesystem hierarchy can be designated as a mount point for another filesystem. If the directory contains files, those files are not deleted but become temporarily inaccessible until the mounted filesystem is unmounted.

While it is common practice to use empty directories as mount points for clarity, it is not a technical requirement; non-empty directories can also be used, though their original contents will be hidden.

Directories do not need to have the SetUID flag set to be used as a mount point; the SetUID flag is related to user execution permissions for executables, not mounting.

Files within a directory used as a mount point are not deleted; they become temporarily obscured by the newly mounted filesystem and reappear once the filesystem is unmounted.