Question

Read the excerpt from "Perseus." The Ethiopians were being devoured in numbers by the serpent; and, learning from the oracle that they could be freed from the pest only if Andromeda were offered up to it, they forced Cepheus, her father, to consent. When Perseus arrived the maiden was on a rocky ledge by the sea, chained there to wait for the coming of the monster. In this excerpt, readers learn that is an accepted practice in ancient Greek life.

Answer 1

the answer is sacrifice 

Answer 2

If the idea is to realize which practice in ancient greek life is accepted from reading this excerpt, the answer would be sacrifice.

The only way for the Ethiopians to stay alive is to offer Andromeda as a gift to the monster. Only by doing that, they could "be freed from the pest".