对于PPT的操作，在标题上添加了文本和图片，怎么让文本置于顶层，不然图片会被覆盖住！

 PowerPoint.Presentation presentation = this.Application.Presentations.Add();
            PowerPoint.CustomLayout customLayout =
                presentation.SlideMaster.CustomLayouts[PowerPoint.PpSlideLayout.ppLayoutTitle];
            PowerPoint.Slide slide = presentation.Slides.AddSlide(1, customLayout);
            string filePath = "C:\\图片1.jpg";
            PowerPoint.Shape pic;
            pic = slide.Shapes.AddPicture(filePath, Office.MsoTriState.msoFalse, Office.MsoTriState.msoTrue
                , slide.Shapes[1].Left, slide.Shapes[1].Top, slide.Shapes[1].Width, slide.Shapes[1].Height);
            pic.Height = slide.Shapes[1].Height;
            pic.Width = slide.Shapes[1].Width;
            slide.Shapes.Title.TextFrame.TextRange.Text = "123456";
            slide.Shapes.Title.TextFrame.TextRange.Font.Color.RGB = Color.Red.ToArgb();
            slide.Shapes.Title.TextFrame.TextRange.Font.Size = 52;
            slide.Shapes[2].Delete();