Final answer:
The past tense of 'turn off' is 'turned off'.
Step-by-step explanation:
The past tense of 'turn off' is 'turned off'.
For example, in a sentence: Yesterday, I turned off the lights before leaving the room.
It is important to remember that in English, regular verbs typically form their past tense by adding '-ed' to the base form of the verb. In this case, 'turn off' is a separable phrasal verb and the past tense is formed by adding '-ed' to the main verb 'turn'.
Learn more about past tense