What could be the possible causes of sadness?? why sadness comes unconditionally sometimes??? xD

The significant structural shift that happens between chapters 21 and 22 is

Sister carrie, chapter ii theodore dreiser how does the author prepare readers for the last full paragraph of this passage? a) the author introduces carrie by showing readers the similarities between carrie and her sister, who is married to a hardworking man. b) the author introduces carrie as the jealous sibling of minnie, who works hard to make carrie feel welcome without upsetting her own marital balance. c) the author introduces carrie as an observant and young woman who notices the routine of her sister and brother-in-law, with whom she is staying. d) the author introduces carrie as a rather selfish and naive young woman who accepts the hospitality of her sister and brother-in-law until she can find a job in the city.

Write a fiction story which give you some moral lesson