A good unit to masher the distance between planets would be?

Where the main factor that enabled the growth of cities and civilizations was the existence of

What conclusion can be drawn about the location of the city of syracuse? it was built on the coastline due to easy access to the red sea. it was built on the coastline due to easy access to the mediterranean sea. it was built inland to protect it from invaders sailing in from the mediterranean sea. it was built inland to protect it from invaders sailing in from the red sea.

This desert is found in the northern part of africa and covers 3.5 million square miles.