input: def list_countries_api(data_path: str) -> None:
      """Create a basic REST API using Python and Flask to list all the countries in the world.
      The API should read the list of countries from a JSON file located at `data_path` and 
      return them as a JSON response when a GET request is made to '/countries'.
      >>> list_countries_api('data.json')
      (No return value, but should start a Flask server serving the API)
      """
output:     from flask import Flask, jsonify
      import json
  
      app = Flask(__name__)
  
      @app.route('/countries', methods=['GET'])
      def get_countries():
          with open(data_path, 'r') as file:
              countries = json.load(file)
          return jsonify(countries)
  
      if __name__ == '__main__':
          app.run(debug=True)