protected override void LoadContent()
        {
            // Create a new SpriteBatch, which can be used to draw textures.
            spriteBatch = new SpriteBatch(GraphicsDevice);
 
            audioEngine = new AudioEngine("Content\\Audio\\TutorialAudio.xgs");
            waveBank = new WaveBank(audioEngine, "Content\\Audio\\Wave Bank.xwb");
            soundBank = new SoundBank(audioEngine, "Content\\Audio\\Sound Bank.xsb");
 
            //建立Camera
            mainCamera = new Camera(this, cameraPosition, cameraLookAt, Vector3.Up);
 
            terrain.model = Content.Load(
                "Models\\terrain");
            //载入坦克模型
            tank.model = Content.Load(
                "Models\\kl");
            tank.scale = 0.08f;
            tank.position.Y += 50;
            tank.position.Z -= 500;
 
            missileLauncherBase.model = Content.Load(
                "Models\\launcher_base");
            missileLauncherBase.scale = 0.2f;
 
            missileLauncherHead.model = Content.Load(
                "Models\\launcher_head");
            missileLauncherHead.scale = 0.2f;
            missileLauncherHead.position = missileLauncherBase.position +
                new Vector3(0.0f, 20.0f, 0.0f);
 
            missiles = new GameObject[numMissiles];
            for (int i = 0; i < numMissiles; i++)
            {
                missiles[i] = new GameObject();
                missiles[i].model =
                    Content.Load("Models\\missile");
                missiles[i].scale = 3.0f;
            }
 
            enemyShips = new GameObject[numEnemyShips];
            for (int i = 0; i < numEnemyShips; i++)
            {
                enemyShips[i] = new GameObject();
                enemyShips[i].model = Content.Load(
                    "Models\\enemy");
                enemyShips[i].scale = 0.1f;
                enemyShips[i].rotation = new Vector3(
                    0.0f, MathHelper.Pi, 0.0f);
            }
 
            // TODO: use this.Content to load your game content here
        }