//Remove everything from screen (READY SCREEN)
    public void clearScreen()
    {
        helpScreen.SetActive(false);
        CancelInvoke();                                          //To not spawn UFO

        player.GetComponent <PlayerCollision>().cancelRespawn(); //Not respawn player accidentally
        player.SetActive(false);
        BigUFO.SetActive(false);
        SmallUFO.SetActive(false);
        BigAsteroids.inactiveAll();
        MedAsteroids.inactiveAll();
        SmallAsteroids.inactiveAll();
    }
    //Where the asteroids and UFO plays in Main Menu
    public void startDemo()
    {
        player.SetActive(false);
        BigUFO.SetActive(false);
        SmallUFO.SetActive(false);

        spawnAsteroids(); //Spawn 4 asteroids

        MedAsteroids.inactiveAll();
        SmallAsteroids.inactiveAll();

        Invoke("spawnUFO", 15f); //Spawn UFO each 15 seconds
    }
    //Gameplay screen
    public void startGameplay()
    {
        player.SetActive(true);
        player.transform.position = new Vector3(0f, 0f); //Set player to the center of the screen

        BigUFO.SetActive(false);
        SmallUFO.SetActive(false);

        spawnAsteroids(); //Spawn 4 asteroids at begining

        MedAsteroids.inactiveAll();
        SmallAsteroids.inactiveAll();

        Invoke("spawnUFO", 15f);
    }