Select the option that expresses the given sentence in active voice.
A machine had been developed by Dr. John Gibbon in the US after twenty years.

Correct option is D

"Dr. John Gibbon had developed a machine in the US after twenty years." represents the given sentence in active voice, accurately conveying the action performed by Dr. John Gibbon.
· Active Voice- Active voice is a grammatical structure in which the subject of the sentence performs the action expressed by the verb.
· Passive Voice- Passive voice refers to a grammatical construction where the subject of a sentence undergoes an action rather than performing it. In passive voice sentences, the emphasis is on the recipient or object of the action.
Conversion rule: Object + auxiliary verb (had) + been + past participle + by + subject -> <- Subject + had + V3 + object.