Microsoft Excel files are also referred to asa.workbooksb.documentc.sheetsd.file

The correct answer is a. workbooks.

In Microsoft Excel, a workbook is the file format that consists of one or more worksheets. Each worksheet is a single tab within the workbook that contains cells organized into rows and columns for data entry and manipulation. Therefore, when you save an Excel file, you are saving it as a workbook which can contain multiple sheets where you can perform various calculations, data analysis, and visual representations of data. The terms "document," "sheets," and "file" may relate to the components and the nature of Excel files, but the specific term used by Microsoft to refer to the complete file is indeed "workbook."

Workbooks can be identified by their file extension, typically ".xlsx" for versions starting from Excel 2007. Understanding this terminology is essential for efficiently working with Microsoft Excel and navigating its features.