Passive Voice: The plane was hijacked.
Explanation:
* Subject: The original sentence has the active subject "they." In the passive voice, the object of the original sentence ("the plane") becomes the subject.
* Verb: The active verb "hijacked" becomes the passive verb "was hijacked."
* By Phrase: The "by phrase" (indicating who did the action) is often optional in passive voice. You could add "by them" to be more explicit, but it's generally understood.
Let me know if you'd like to practice with other sentences!