How does this sentence demonstrate an unusual use of syntax? the boy did what? it ends with a question mark but is not a question. the subject comes before the predicate. it is not a complete sentence. the traditional syntax has been inverted, or reversed.

Based on the given sentence above, I can say that what makes its use of syntax unusual is that the traditional syntax has been inverted, or reversed. Given that the sentence is in a question form, using the traditional syntax, it would be like this: "What did the boy do?" The answer to this is the last option. Hope this helps.