All lines that start with a '#' are comments

#  Make a /etc/apt/preferences file and populate it
#  "sudo touch /etc/apt/preferences
#  Now, open that file woth your fav editor and populate it 
#  with ths lines below

Package: *
Pin: release a=stable
Pin-Priority: 900
Package: *
Pin: release a=testing
Pin-Priority: -10