deb-src  http://ftp.de.debian.org./debian   buster                  main contrib non-free
deb-src  http://ftp.de.debian.org./debian   buster-updates          main contrib non-free
deb-src  http://ftp.de.debian.org./debian   buster-proposed-updates main contrib non-free
deb-src  http://security.debian.org./       buster/updates          main contrib non-free
# deb-src  http://ftp.de.debian.org./debian   buster-backports        main contrib non-free