Final answer:
The feature that lets collaborators see updates since they last viewed the sheet is 'Highlight changes.' It is useful for tracking edits in a shared document.
Step-by-step explanation:
Changes in cell formatting can indeed be used to highlight updates or important information in a spreadsheet. Among the options provided, the feature that allows collaborators to see updates since they last viewed the sheet is d) Highlight changes. This feature is often found in collaborative spreadsheet applications such as Sheets. When enabled, it highlights the cells that were edited since the last time a user accessed the document, making it easier for collaborators to track changes and updates. On the other hand, conditional formatting changes the appearance of cells based on set rules, format painter copies formatting from one cell to another, and a symbol column type is relevant for identifying types of data but does not track or highlight changes for users.