What did the ancient indus valley, huang, and nile civilizations have in common?

they built pyramids to reach the gods.
they elected leaders using potsherds.
they developed and used gunpowder.
they began in fertile river valleys.

Which describes a contribution from classical rome to modern western civilization? a. international gathering to celebrate sporting achievement b. written constitution based on natural rights c. large infrastructure projects to benefit the public d. direct election of the ruler by all residents of the empire