Question

had you won the first prize in passive voice​

Answer 1

Answer:

had the first prize been win by you.

Answer 2

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Had the first prize been won by you ?

Structure ↴

Had + Subject + been + past participle form of the main verb + by + Object + question mark (?)

Explanation ↴

The given sentence is a simple structure of interrogative sentence of past perfect tense. To convert Interrogative Sentences of Past Perfect to Passive Voice, we put had as the subject of the sentence and use a Question mark (?) after the Object.