machu picchu ruins may have been built by the incas. the incas might have built machu picchu ruins....

Machu Picchu ruins may have been built by the Incas.

The Incas might have built Machu Picchu ruins. ( Perfect Modal in the active voice)

( Perfect Modal in the passive voice)

Grammar. Perfect modals in the passive voice for speculating about the past.

Macchu Picchu Ruins

Aliens could have made The Nazca Lines.

The Nazca Lines could have been made by aliens.

The Nazca

Lines

(Active voice)

(Passive voice)

The storm The car accident

Verb : cause The car accident must have been caused by the storm. (Passive)

The storm must have caused the car accident. (Active)

Short responses with perfect modals in the passive voice

A:Do you think dinosaurs were killed by a meteor?

B: They might have been.B: They had to have been.

The dinosaurs might (or may) have been killed by a meteor. The trees could have been destroyed by a fire.The gold figures might not (or may not have been lost.

The stone balls must have been moved by animals.The drawings must not have been discovered until later.

The crater had to have been caused by a meteorite.

The trees couldn’t have been burned by a fire.