The correct answer is D. WK1.
Lotus 1-2-3 is a spreadsheet program that was developed by Lotus Development Corporation in 1983. It was one of the first spreadsheet programs to be widely used, and it helped to popularize the use of spreadsheets in business and personal computing.
Files created with Lotus 1-2-3 have a .wk1 extension. This extension is used to identify files that are created with Lotus 1-2-3. Other spreadsheet programs, such as Microsoft Excel, use different extensions for their files.
The other options are incorrect. A. DOC is the extension for Microsoft Word documents. B. XLS is the extension for Microsoft Excel spreadsheets. C. 123 is not a valid file extension.