input: from typing import Dict
  import flask
  from flask import Flask, request, jsonify
  import json
  
  app = Flask(__name__)
  
  @app.route('/countries', methods=['GET'])
  def get_countries() -> Dict:
      """This function returns a JSON response containing a list of all the countries in the world.
      >>> with open('data.json', 'r') as f:
      ...     countries = json.load(f)
      >>> get_countries() == jsonify(countries)
      True
      """
      with open('data.json', 'r') as f:
          countries = json.load(f)
      return jsonify(countries)
  
  if __name__ == '__main__':
      app.run()
output:     with open('data.json', 'r') as f:
          countries = json.load(f)
      return jsonify(countries)