Why do I get the error message: NoMethodError in StaticPagesController#index

When I run ruby on rails program, get the error message:undefined method `action' for StaticPagesController:Class

application_controller.rb

require_relative '../models/pet'

class ApplicationController < Sinatra::Base


  get '/' do
    #home
    erb :index
  end
  get '/questions' do
    erb :questions
  end
post '/results' do 
  @dog=get_results(params)

  erb :results
end
end

Here is my static_pages_controller.rb

class StaticPagesController < ApplicationController

  def index
     # Renders static_pages/swalton2html.erb by default.
  end

   def questions
    # Renders static_pages/swalton2html.erb by default.
  end