input: Write a function to connect to MySQL, MongoDB, and PostgreSQL databases, execute predefined queries, fetch the results, close the connections, and render the results on a web page. The function should take no arguments and return the rendered webpage.
  
  assert render_page().render('template.html')=={'data_mysql': result_mysql, 'data_mongodb': result_mongodb, 'data_postgresql': result_postgresql}
output: def render_page():
      import mysql.connector
      from pymongo import MongoClient
      import psycopg2
      from jinja2 import Template
  
      # MySQL connection and query
      mysql_conn = mysql.connector.connect(host='localhost', user='root', password='password', database='mysql_db')
      mysql_cursor = mysql_conn.cursor()
      mysql_cursor.execute("SELECT * FROM table_name")
      result_mysql = mysql_cursor.fetchall()
      mysql_cursor.close()
      mysql_conn.close()
  
      # MongoDB connection and query
      mongo_client = MongoClient('localhost', 27017)
      mongo_db = mongo_client['mongodb_db']
      mongo_collection = mongo_db['collection_name']
      result_mongodb = list(mongo_collection.find())
      mongo_client.close()
  
      # PostgreSQL connection and query
      postgresql_conn = psycopg2.connect(host='localhost', database='postgresql_db', user='postgres', password='password')
      postgresql_cursor = postgresql_conn.cursor()
      postgresql_cursor.execute("SELECT * FROM table_name")
      result_postgresql = postgresql_cursor.fetchall()
      postgresql_cursor.close()
      postgresql_conn.close()
  
      # Render the results on a web page
      def render(template_file):
          with open(template_file, 'r') as file:
              template = Template(file.read())
          return template.render(data_mysql=result_mysql, data_mongodb=result_mongodb, data_postgresql=result_postgresql)
  
      return render