The correct answer is 4.File extensionThe width of the file extension in MS Word 2007 has 4 characters.A file extension is a shortened form of the file type at the end of a file name.These extensions determine your documents file type, and the file type determines what programs can open the file.While most programs can read most file types, not every program can read every file type.The default file type is .docx (Word Document). This file extension works in most Microsoft Word programs.However, there may be times when you want to save a different file type.Additional InformationA subscript is a number, figure, symbol, or indicator that is smaller than the normal line of type and is set slightly below it.For ex- Formula of Carbon Dioxide is CO2.The shortcut key to create subscript in MS-Word is Ctrl + =.A superscript is a number, figure, symbol, or indicator that is smaller than the normal line of type and is set slightly above it.For ex- ion of sodium is Na?+1.For superscript, press Ctrl, Shift, and the Plus sign (+) at the same time.Important PointsShortcutPurposeAlt + SInsert the current date.Alt + =Create the formula to sum all of the above cellsCtrl + SSave