Which one of the following sentences is not in passive

Solution

Sentences in the passive voice follow the structure Object + past participle of the verb + by agent (optional). The agent, who performs the action, is usually introduced with "by." In sentence 3, "mouse" is the subject, not the object, and it describes the role it plays in relation to the cat. It defines the natural relationship between the two animals, not an action being performed on the mouse. Therefore, it's not passive voice.