Under is a preposition.
Prepositions are words that indicate location. It tells the location of the subject or object.
Prepositions not only show the actual location of a place but also the location in time.
Some prepositions of an actual location are: in, on, under, above, behind, beside, etc.
Some prepositions of a location in time are: before midnight, after the exams, during winter....
Answer:
"'Nothing Gold Can Stay' is a short poem written by Robert Frost. The poem deals with the idea of impermanence, life and death. Frost uses paradox, juxtaposition, and personification in the poem to emphasize his messages. The poem is a composed of four rhyming couplets."
Explanation:
https://study.com/academy/lesson/robert-frosts-nothing-gold-can-stay-poem-meaning-analysis.html