The line of the poem which expresses the theme that youth passes quickly is:
“ But only so an hour”
The poem “Nothing Gold Can Stay,” by Robert Frost is about the inevitability of things which are beautiful and soothing. Frost explores the theme that although youth is beautiful and charming, it will be lost someday. He shows this change with the examples taken from nature. He adds that the flowers which bloom in spring season will be lost and the children will grow and turn into adults. He takes the example of the Fall of man to show that every beautiful thing can be turned down.
A) The urbanization of the United Stats quickened due to technology improvements.
-This whole paragraph is on the subject of how technology quickly urbanized the United States. All of the other answers are factors that caused this to happen.