past possibilities

There's no evidence or research confirming the age of the artifact yet. It MUST HAVE/MIGHT HAVE been from the medieval era.

Scientists are still debating about how the stones were moved to build the pyramids in Egypt. Some believe that the pyramid workers MUST HAVE/MAY HAVE pushed and rolled the stones

Some people believe that aliens MAY HAVE/MUST HAVE helped the Egyptians build the pyramids thousands years ago.

I MAY HAVE/MUST HAVE gone completely white because my friends knew something was wrong with me right away.

There 's a possibility that prehistoric people MIGHT HAVE/MUST HAVE built the pyramid structure of Gunung Padang 20,000 years ago.

A ghost COULDN'T HAVE/MAY HAVE stolen your watch. You MUST HAVE/COULDN'T HAVE forgotten where you had put it.

The creature I saw yesterday looked like a dog, but it had spikes on its bag. It COULDN'T HAVE/MUST HAVE been a dog. Dogs don't have spikes on their backs

People saw the river turn red yesterday. Wastes from a nearby factory MAY HAVE/MUST HAVE caused it. The police are still investigating the phenomenon.

I think I saw Bigfoot crossing the street in front of me last night, but I'm not sure. I MUST HAVE/MIGHT HAVE seen a big bear.

I heard my grandma's voice in my room last night. I MUST HAVE/MUSTN'T HAVE been dreaming because my grandma passed away years ago.