What is done cannot be undone,?(tag question)

The answer to this tag question is: Can it?

A tag question is also referred to as a question tag and it can be defined as a very short clause placed at the end of a sentence (statement), which typically changes it to a question.

Basically, a tag question is used to elicit, educe, or evoke affirmation for a sentence (statement) from a respondent i.e the person whom you're talking to. Also, a tag question always appear at the end of a sentence (statement) and a comma is used to separate it from the clause.

Some examples of tags used in English language are: can we, can't we, should I, aren't they, shouldn't they, wouldn't it, weren't they, do I, shall we, can it, etc.

As a general rule, a positive sentence requires a negative tag question while a negative sentence (statement) requires a positive tag question.

In this scenario, we have a negative sentence (statement) and as such we should use a positive question tag (can it).

In conclusion, a tag question must always refer to the subject of a sentence (statement).

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You cannot change what has already happened or come to pass, so there's no use worrying or stressing about it; what's done is done.

Explanation: