Read “nothing gold can stay” by robert frost. what is the literal meaning of 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.

a. sunset and sunrise are the shortest parts of the day.
b. many different colors exist in the natural world.
c. the elements one notices in the natural world do not last long.
d. the color of a leaf changes depending on the time of day.