You want to append a tar file if the on-disk version of the tar file...

The tar -u command is used to append a tar file if the on-disk version of the tar file has a modification date more recent than its copy in the tar archive.

Answer option B is incorrect. The tar -t command is used to list the contents of an archive.

Answer option A is incorrect. The tar -x command is used to extract the files from an archive.

Answer option D is incorrect. The tar -c command is used to create a new archive of specified files.