input: Write a response that appropriately completes the request.
  
  ### Instruction:
  Create a basic REST API using Python and Flask to list all the countries in the world.
  
  ### Input:
  Not applicable
  
  ### Output:
  import flask
  from flask import Flask, request, jsonify
  import json
  
  app = Flask('name')
  
  @app.route('/countries', methods=['GET'])
  def get_countries():
      with open('data.json', 'r') as f:
          countries = json.load(f)
      return jsonify(countries)
  
  if 'name' == 'main':
      app.run()
output: def get_countries():
      with open('data.json', 'r') as f:
          countries = json.load(f)
      return jsonify(countries)