input: Write a function to create an interactive text-based RPG game in Python where the player can move between rooms and engage in battles with monsters. The game should include classes for the Player, Room, and Monster, and should have a main game loop where the player can choose actions like moving to another room or fighting monsters in the current room. If the player's health drops to 0 or below, the game should end with a defeat message.
  
  class Player(object):
   def __init__(self):
   self.health = 100
   self.location = 'room one'
   self.monsters_killed = 0
  
  class Room(object):
   def __init__(self):
   self.name = ''
   self.description = ''
   self.monsters = []
  
   def add_monster(self, monster):
   self.monsters.append(monster)
  
  class Monster(object):
   def __init__(self):
   self.name = ''
   self.health = 100
  
   def attack(self, player):
   player.health -= 10
  
  def start_game():
   player = Player()
  
   while True:
   print(f'You are in {player.location}.')
   print('Available actions: move, fight')
   response = input('What would you like to do? ').lower()
  
   if response == 'move':
   # Move the player to the chosen room
   pass
  
   if response == 'fight':
   # Initiate a battle between the player and the monster
   pass
  
   if player.health <= 0:
   print ('You have been defeated!')
   break
  
  if __name__ == '__main__':
   start_game()
  
  assert start_game().__name__ == 'start_game'
  assert Player().health == 100
  assert Room().monsters == []
  assert Monster().attack(Player()) == None, 'Player health should be reduced'
output: def start_game():
      player = Player()
      rooms = {
          'room one': Room(),
          'room two': Room(),
          'room three': Room()
      }
      rooms['room one'].add_monster(Monster())
      rooms['room two'].add_monster(Monster())
  
      while True:
          print(f'You are in {player.location}.')
          print('Available actions: move, fight')
          response = input('What would you like to do? ').lower()
  
          if response == 'move':
              new_location = input('Where would you like to move? (room one, room two, room three) ').lower()
              if new_location in rooms:
                  player.location = new_location
              else:
                  print('Invalid room!')
  
          if response == 'fight':
              current_room = rooms[player.location]
              if current_room.monsters:
                  monster = current_room.monsters[0]
                  print(f'You are fighting a monster in {player.location}!')
                  while monster.health > 0 and player.health > 0:
                      monster.attack(player)
                      print(f'Monster attacks! Your health is now {player.health}.')
                      if player.health <= 0:
                          print('You have been defeated!')
                          return
                      player_attack = input('Attack the monster? (yes/no) ').lower()
                      if player_attack == 'yes':
                          monster.health -= 20
                          print(f'You attack the monster! Its health is now {monster.health}.')
                  if monster.health <= 0:
                      print('You have defeated the monster!')
                      current_room.monsters.remove(monster)
                      player.monsters_killed += 1
              else:
                  print('No monsters in this room!')
  
          if player.health <= 0:
              print('You have been defeated!')
              break