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