Question

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?

Answer 1

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

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