I NEED HELP ASAP

What is the main idea presented in this passage?

[In about 1200, a] major population shift saw [the Ancestral
Puebloans] begin to move back into the cliff alcoves [or
recesses] that sheltered their ancestors centuries before.
Why did they make this move? We don't know. Perhaps it
was for defense; perhaps it was for religious or
psychological reasons; perhaps alcoves offered better
protection from the elements. Whatever the reason, or
reasons, it gave rise to the cliff dwellings for which Mesa
Verde is most famous.1
OA. Mesa Verde is famous for its Ancestral Puebloan cliff dwellings.

A. Mess Verde is famous for its Ancestral Puebloan cliff dwellings.

B. The Ancestral Puebloan population shifted many times throughout history.

C. Cliff dwellings made it easier for the Ancestral Puebloan to defend themselves.

D. The Ancestral Puebloan moved into cliff dwellings for unknown reasons.