input: Write a function to implement an interactive text-based RPG game in Python that allows a player to move around in an environment and battle monsters. The game should include a Player class, a Room class, and a Monster class. The game should have a main loop where the player can choose actions such as moving to a new room or fighting monsters in the current room. If the player's health falls to zero or below, the game should end.
  assert start_game()==None
  assert type(Player())==Player
  assert type(Room())==Room
  assert type(Monster())==Monster
output: def start_game():
      class Player:
          def __init__(self):
              self.health = 100
              self.inventory = []
  
          def take_damage(self, damage):
              self.health -= damage
              if self.health <= 0:
                  print("Game Over")
                  return True
              return False
  
      class Room:
          def __init__(self):
              self.monsters = [Monster() for _ in range(2)]
  
          def is_empty(self):
              return len(self.monsters) == 0
  
      class Monster:
          def __init__(self):
              self.health = 20
  
          def take_damage(self, damage):
              self.health -= damage
              return self.health <= 0
  
      def battle(player, room):
          while not room.is_empty():
              monster = room.monsters.pop()
              while monster.health > 0:
                  print("A monster attacks!")
                  if player.take_damage(5):
                      return
                  monster.take_damage(10)
                  print("You defeated a monster!")
  
      player = Player()
      current_room = Room()
  
      while True:
          print("1. Move to a new room")
          print("2. Fight monsters in the current room")
          choice = input("Choose an action: ")
  
          if choice == "1":
              current_room = Room()
              print("You moved to a new room.")
          elif choice == "2":
              if current_room.is_empty():
                  print("The room is empty.")
              else:
                  battle(player, current_room)
          else:
              print("Invalid choice. Try again.")