Displaying a comment box on customized ActiveAdmin Show page

I'm using ActiveAdmin. By default, the comment box will appear at the bottom of the show page, but after I customize it that comment box block disappears.

ActiveAdmin.register Book do
  scope :all, :default => true
  scope :publish

  show do
    attributes_table :name, :description, :owner, :company, :publish, :publisher
  end 
end

How can I add the comment box back to the show page?