Select the option that expresses the given sentence in passive voice.

The judge found the prisoner guilty.

The prisoner was found guilty by the judge. 

The correct passive voice form of the sentence "The judge found the prisoner guilty" is The prisoner was found guilty by the judge.

The active voice of the sentence is "The judge found the prisoner guilty." This sentence is in the simple past tense, which is used to describe an action that happened in the past. The passive voice of the sentence is formed by putting the subject of the active sentence after the verb "to be" and the past participle of the main verb. In this case, the subject of the active sentence is "judge" and the main verb is "find." The past participle of "find" is "found." So, the passive form of the sentence is "The prisoner was found guilty by the judge."

The other options are incorrect because:

• The prisoner had been found guilty by the judge. This sentence is in the past perfect tense, which is used to describe an action that happened in the past before another action happened. However, in this case, the action of the prisoner being found guilty is not relevant to the present.
• The judge was found guilty by the prisoner. This sentence is the opposite of the active sentence, and is therefore incorrect.
• The prisoner has been found guilty by the judge. This sentence is in the present perfect tense, which is used to describe an action that has happened in the past and is still relevant to the present. However, the action of the prisoner being found guilty is not happening now.