Concept:A spreadsheet formula must begin with a special symbol so the application recognises it as a calculation.Explanation:In spreadsheet applications such as Microsoft Excel, LibreOffice Calc, or Google Sheets, typing = at the start of a cell tells the application that a formula follows.For example, typing =5+3 in a cell calculates and displays 8, while typing just 5+3 would show the text 5+3.Therefore, the correct sign is the equals sign.Answer:D. =