1. It's no use worrying about it.

2. It's no use to worry about it.

3. It's of no use worrying about it.

4. It's of no use to worry about it.
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Which ones are grammatical? What does 'it' in the front refer to in each sentence?

1 answer

All are correct, but I wouldn't use this phrasing.

I'd change the beginning of each sentence to "There's no use worrying ... "