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(10a) When will you take out that trash?

1. Sentence (10a) is a wh-question and presupposes the truth of the proposition it expresses, 'You will take out that trash.'

2. Sentence (10a) is a wh-question and presupposes the truth of the proposition: 'You will take out that trash', it expresses.

3. Sentence (10a) is a wh-question and presupposes the truth of the proposition, 'You will take out that trash', it expresses.

I found the sentence #1 in my book.

Q) Can I change the structure like #2 and #3?(can they be considered as other ways to express the same idea?)
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No, #2 and #3 are poorly structured.
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1. Sentence (10a) is a wh-question and presupposes the truth of the proposition it expresses, 'You will take out that trash.'

I don't know what 'it' refers to.

Do you know what 'it' refers to in this sentence?
'It' is the question. The question expresses (though perhaps 'express' is not a good word choice; 'implies' would be more correct) the truth of the proposition 'You will take out the trash'.