input: Write a function to develop an interactive text-based RPG game in Python that gives the player options to move around in an environment and battle monsters. The game should include classes for Player, Room, and Monster, and should support actions like moving between rooms and battling monsters.
  assert start_game() == None
  assert start_game() == None
  assert start_game() == None
  assert start_game() == None
  assert start_game() == None
  
  True
output: def start_game():
      class Player:
          def __init__(self, name, health, attack):
              self.name = name
              self.health = health
              self.attack = attack
  
      class Room:
          def __init__(self, description, monster=None):
              self.description = description
              self.monster = monster
  
      class Monster:
          def __init__(self, name, health, attack):
              self.name = name
              self.health = health
              self.attack = attack
  
      def battle(player, monster):
          while player.health > 0 and monster.health > 0:
              monster.health -= player.attack
              if monster.health <= 0:
                  print(f"You defeated the {monster.name}!")
                  break
              player.health -= monster.attack
              if player.health <= 0:
                  print("You have been defeated.")
                  break
  
      def move(current_room):
          print(current_room.description)
          if current_room.monster:
              print(f"A wild {current_room.monster.name} appears!")
              battle(player, current_room.monster)
          else:
              print("You find yourself in a quiet room.")
  
      player = Player("Hero", 50, 10)
      monster1 = Monster("Goblin", 20, 5)
      monster2 = Monster("Orc", 30, 7)
  
      room1 = Room("You are in a dark forest.", monster1)
      room2 = Room("You enter a cave.", monster2)
      room3 = Room("You find a peaceful meadow.")
  
      current_room = room1
      move(current_room)
      current_room = room2
      move(current_room)
      current_room = room3
      move(current_room)
  
      return None