Something

debian:~# apt-cache policy base-passwd
base-passwd:
  Installed: 3.5.9
  Candidate: 3.5.11
  Version Table:
     3.5.11 0
        650 http://the.earth.li testing/main Packages
        600 http://the.earth.li unstable/main Packages
 *** 3.5.9 0
        500 http://the.earth.li sarge/main Packages
        100 /var/lib/dpkg/status
debian:~# cat /etc/apt/preferences
Package: *
Pin: release a=sarge
Pin-Priority: 700

Package: *
Pin: release a=testing
Pin-Priority: 650

Package: *
Pin: release a=unstable
Pin-Priority: 600