Final answer:
The 'Undo' function is the tool used to reverse the last grammatical change made in a document, unlike 'Redo' which reverses the undo action, and 'Cut' and 'Paste' which remove and insert text respectively.
Step-by-step explanation:
The option that enables you to undo the last grammatical change is A) The "Undo" function. The Undo command is a quick and efficient way to correct mistakes or changes that you have just made. On the other hand, B) "Redo" reverses the undo action, C) "Cut" removes the selected text from the document, and D) "Paste" inserts text or data that has been copied or cut.