The passive voice is form with: the modal+ have+been+past paticiple of the verb

The active voice is form with the modal+have +been+past participle of the verb.

Is this sentece correct or incorrect?It might have been a ghost or a hostile entity.

Hunters could have been killed lions and bears on the forest.

Whywas Tomas late to class  on Monday?

He couldn’t have forgotten toset his alarm clock.

The figures must had been very important

Some envelops could have been delivered.

John wasn’t in class today.  I wonder why . ..

I wonder why the students didn't come to class.

This document ____ ____destroyed. We had to cover up all the traces of this deal.

Success ____ be achieved if you had worked very hard and never given up, but you didn't.

We ______________ a better result if we hadn't forgotten the answers.