请高手过来看看这个代码怎么错了

  在VS2010中brushs，td，td1总是下面画红线，显示上下文没有此变量，该怎么改啊？？？private void Form1_Load(object sender, System.EventArgs e)
        {
            //点颜色数组的创建
            brushs=new Brush[4];//实例颜色数组    
            //添加颜色到数组
            brushs[0]=Brushes.Red;
            brushs[1]=Brushes.Yellow;
            brushs[2]=Brushes.Blue;
            brushs[3]=Brushes.Green;
            //颜色的数组创建
            colors = new Color[4]{Color.Red,Color.Blue,Color.Yellow,Color.Green};
            td=new Thread(new ThreadStart(ShowP));//创建线程对象确定随机生成点的方法
            td1=new Thread(new ThreadStart(ShowL));//创建线程对象确定动态显示标签的方法
            td.Start();
            td1.Start();            
        }
        //随机生成点的方法
        private void ShowP()
        {
            Random rnd=new Random();
            int r=0;//保存数组下标
            int positionx=0;//保存点的X坐标
            int positiony=0;//保存点的Y坐标 
            while(true)
            {
                Graphics g=this.CreateGraphics();
                r=rnd.Next(0,4);
                positionx=rnd.Next(0,this.Width);
                positiony=rnd.Next(0,this.Height);
                g.FillEllipse(brushs[r],positionx,positiony,8,8);//绘制点
                Thread.Sleep(100);
            }
        }        //动态显示标签的方法
        private void ShowL()
        {
            Random rnd=new Random();
            int x=this.label1.Left;//获取标签的原位x坐标
            int y=this.label1.Top;//获取标签的原位y坐标
            int colorIndex;
            while(true)
            {
                for(int i=0;i<3;i++)
                {
                    colorIndex=rnd.Next(0,4);
                    this.label1.Left+=1;
                    this.label1.Top+=1;
                    this.label1.ForeColor=colors[colorIndex];
                    Thread.Sleep(100);
                }
                this.label1.Left=x;
                this.label1.Top=y;
            }        }        private void Form1_Closed(object sender, System.EventArgs e)
        {
            td.Abort();
            td1.Abort();
        }