Answer:
Passive
Step-by-step explanation:
The passive voice is made up of the appropriate form of the verb "to be" + the past participle of the main verb. This type of voice is used to put emphasis on who or what receives or experiences an action instead of the one who performs the action.
The sentence provided uses the passive voice because it uses the appropriate form of the verb "to be" for "we" and the simple past tense: "were" and the past participle of the verb "leave": "left"; and it puts the focus on the people who were left: "we", and not on the person that performed the action: "the teacher."