The correct answer is .doc.The DOCX and DOC file extensions are used for Microsoft Word documents, part of the Microsoft Office Suite of software.XLSM is the file extension that is assigned to spreadsheets created by Microsoft Excel 2007 and newer. They are saved using the Open XML standard. PNG is short for Portable Network Graphic, a type of raster image file. It's particularly popular file type with web designers because it can handle graphics with transparent or semi-transparent backgrounds.A TXT file is a standard text document that contains plain text. It can be opened and edited in any text-editing or word-processing program.