StringGrid控件的问题

在StringGrid中，用鼠标拖动选择了多row，在程序中如何知道那些row被选中了？谢谢！

The following code selects the rectangle containing rows 1 through 4, and columns 2 and 3.

void __fastcall TForm1::Button1Click(TObject *Sender)

{
  TGridRect myRect;
  myRect.Left = 3;
  myRect.Top = 1;
  myRect.Right = 2;
  myRect.Bottom = 4;
  DrawGrid1->Selection = myRect;
}