Ruby class definition scoping

scope.rb

class A
  a = "DERP"
  @a = "BARF"
  @@a = "FETUS"

  puts a
  puts @a
end

class A
  puts @a
  begin
    puts a
  rescue Exception => e  
    puts e.message
  end
end

class B < A
  puts "#{@a} -- blank"
  puts @@a
end

class C < B
  puts @@a
end