belongs_to through associations

You can also delegate:

class Company < ActiveRecord::Base
  has_many :employees
  has_many :dogs, :through => :employees
end

class Employee < ActiveRescord::Base
  belongs_to :company
  has_many :dogs
end

class Dog < ActiveRecord::Base
  belongs_to :employee

  delegate :company, :to => :employee, :allow_nil => true
end

Just use has_one instead of belongs_to in your :through, like this:

class Choice
  belongs_to :user
  belongs_to :answer
  has_one :question, :through => :answer
end

Unrelated, but I'd be hesitant to use validates_uniqueness_of instead of using a proper unique constraint in your database. When you do this in ruby you have race conditions.