The correct answer is B. .docx.
A .docx file is a Microsoft Word document created in the Office Open XML (OOXML) file format. It is the default format for Word documents in Microsoft Office 2007 and later versions. .docx files are more efficient than previous versions of Word documents, such as .doc files, and they can be opened and edited by a variety of software programs.
A .pdf file is a Portable Document Format file. It is a type of document file that is designed to be independent of the software, hardware, or operating system used to create or view it. .pdf files are often used to distribute documents that need to be viewed or printed on a variety of devices.
A .txt file is a text file. It is a type of file that contains only text, without any formatting. .txt files are often used to store data or information that needs to be easily read or edited.
An .xls file is an Excel spreadsheet file. It is a type of file that contains data that is organized in a table format. .xls files are often used to store financial data, sales data, or other types of data that needs to be analyzed or calculated.