Which line from Frost's poem "Nothing Gold Can Stay" is an example of an allusion?

So Eden sank to grief

Her hardest hue to hold

Her early leaf's a flower

But only so an hour

So Eden sank to grief

An allusion is a reference to another literary work. In this line Frost is alluding to the place of Eden described in the Bible. Eden is a place of perfection. By saying that "Eden sank to grief", Frost is showing that even a place as perfect as Eden cannot stay forever. She tries to hold on but can't. Throughout the poem, Frost is showing how things that are 'gold' or "good" do not last, things change, and even die.