以下哪些方式能获得Graphics对象obj？ A: Graphics obj = 窗体或控件名.CreateGraphics(); B: private void 窗体或控件名_Paint(object sender, PaintEventArgs e){ Graphics obj = e. Graphics;} C: Bitmap map = new Bitmap(宽,高);Graphics obj = Graphics.FromImage(map);obj.DrawImage(map, x坐标, y坐标); D: Graphics obj = new Graphics(宽,高);