We must have obeyed our teachers.
Answer with explanationAnswer: Option C
If we have “Subject + Modal Auxiliary verb + have + third verb + object”
then we change it to
Passive subject + Modal Auxiliary verb + have been + third form + by + passive object.
Modal Auxiliary verb are : can, could, shall, will, may, might, should, would, must, ought to etc.
Our task had been completed before sunset.
Answer with explanationAnswer: Option D
We had completed our task before sunset.
The given sentence is in passive voice and it is in Past Perfect Tense.
To convert it into active voice, we just remove been from the given sentence and object (our)will be change into subject (We).
Subject + had + V3 + Other agents.
The peon refused him admittance.
Answer with explanationAnswer: Option A
He was refused admittance by the peon.
Given sentence is in Past simple tense and it is in active voice, we need to change it into passive voice.
Subject + (was / were) + V3 + Optional Agents.