求教ActiveX 二次开发AutoCAD的问题

用C#语言基于ActiveX二次开发AutoCAD时，想实现选择CAD界面的一个圆，能返回程序中该圆的原点坐标。希望大神们教教我！

Document doc = Application.DocumentManager.MdiActiveDocument;
Editor ed = doc.Editor;
PromptSelectionResult selectionRes = ed.SelectImplied();
PromptSelectionOptions selectionOpts = new PromptSelectionOptions();
selectionOpts.MessageForAdding = "\n选择圆: ";
selectionRes = ed.GetSelection(selectionOpts);
if (selectionRes.Status == PromptStatus.OK)
{

SelectionSet SS = selectionRes.Value;
ObjectId[] idArray = SS.GetObjectIds();
for (int i = 0; i < idArray.Length; i++)
{
    if(Tools.GetDBObject(idArray[i]).ObjectName == "AcDbCircle" )
    {
            AcadCircle circle = (AcadCircle)Tools.GetDBObject(idArray[i]);
            double[] d= (double[])circle.Center;
            String s="圆心坐标是：" + "X= " + d[0] + "   Y= " + d[1] + "   Z= " + d[2] ;
      }
}

}