Answer:
They cannot live in the ruined environment of the earth.
Step-by-step explanation:
Arthur C. Clarke's stories are usually science fiction stories where planet earth was destroyed by man's extreme exploitation and selfishness. In these stories, the earth has become a planet without the natural resources responsible for our survival, so there is no longer a possibility for humans to live in the destroyed environment that has become our planet. For this reason, people live in colonies, they cannot live in the ruined environment of the earth.