Final answer:
In the post-World War I era, young women rejected traditional appearance and lifestyle and embraced a new morality by adopting the dress and behaviors of flappers.
Step-by-step explanation:
The social changes in the post-World War I era led to young women rejecting traditional appearance and lifestyle. They embraced a new morality and adopted the dress and mannerisms of a flapper, which included wearing shorter skirts, shorter hair, more makeup, and engaging in behaviors considered unladylike at the time, such as drinking and smoking. This rebellious attitude towards traditional values and lifestyle was a significant aspect of the cultural shift in the 1920s.