* Past participle: This is the most common use, acting as part of a passive voice construction. For example: "The patient was treated for a cold." Here, "treated" is part of the passive verb phrase "was treated".
* Past tense: "I treated myself to a new book." Here, "treated" is used in the simple past tense to describe a completed action.
* Adjective: While less common, "treated" can be used as an adjective, especially in a specific context related to wood or materials. For example: "The treated wood was resistant to rot." Here, "treated" describes the wood.
To determine which type of verb "treated" is, you need to consider the entire sentence and the context it is used in.