What does the color "gold" represent in the poem ?

This is the poem

Nature’s first green is gold,


Her hardest hue to hold.


Her early leaf’s a flower;


But only so an hour.


Then leaf subsides to leaf.


So Eden sank to grief,


So Dawn goes down to day.

Nothing gold can stay.


This is the option

A. The speaker's greed

B. The speaker's dreams

C. The slow passage of time

D. The fleeting nature of beauty.

Please no links I need help really bad! I know it not C by the way