text: public String[] GetExternalBookAndSheetName(int extRefIndex){int ebIx = _externSheetRecord.GetExtbookIndexFromRefIndex(extRefIndex);SupBookRecord ebr = _externalBookBlocks[ebIx].GetExternalBookRecord();if (!ebr.IsExternalReferences){return null;}int shIx1 = _externSheetRecord.GetFirstSheetIndexFromRefIndex(extRefIndex);int shIx2 = _externSheetRecord.GetLastSheetIndexFromRefIndex(extRefIndex);String firstSheetName = null;String lastSheetName = null;if (shIx1 >= 0){firstSheetName = ebr.SheetNames[shIx1];}if (shIx2 >= 0){lastSheetName = ebr.SheetNames[shIx2];}if (shIx1 == shIx2){return new String[] {ebr.URL,firstSheetName};}else{return new String[] {ebr.URL,firstSheetName,lastSheetName};}}