The sentence that best describes the symbolic meaning of gold in the poem is The wonderful things in life that do not last.
This poem uses a very important parallel where it shows the word Gold as a precious or perfect thing in this line "Nothing gold can stay". We have another example that talks about how things that we appreciate in life are not eternal and we have to live them when they are happening in the line "Nature's first green is gold".
The other options are not possible because the poem has a constant element of transition from one thing to another which represents temporal things.