text: public ExternalSheet GetExternalSheet(int externSheetIndex){String[] extNames = linkTable.GetExternalBookAndSheetName(externSheetIndex);if (extNames == null){return null;}if (extNames.Length == 2){return new ExternalSheet(extNames[0], extNames[1]);}else{return new ExternalSheetRange(extNames[0], extNames[1], extNames[2]);}}