1. The Incas might have built Machu Picchu ruins.
Grammar. Perfect modals in the passive voice
for speculating about the past.
Macchu Picchu Ruins
The Incas might have built Machu Picchu ruins.
( Perfect Modal in the active voice)
Machu Picchu ruins may have been built by
the Incas.
( Perfect Modal in the passive voice)

2. Aliens could have made The Nazca Lines. (Active voice)
The Nazca Lines could have been made by
aliens.
(Passive voice)

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

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

5. NOT CERTAIN ALMOST CERTAIN
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.
ALMOST CERTAIN
The stone balls must have been moved by
animals.
The drawings must not have been discovered
until later.

6. The crater had to have been caused by a meteorite.
VERY CERTAIN
The crater had to have been caused by a meteorite.
The trees couldn’t have been burned by a fire.