Which of the following might be a possible reason for Bartleby'；s mental disorder considering the historical background？

Which of the following might be a possible reason for Bartleby'；s mental disorder considering the historical background？
A.World War I'；s harm to civilians
B.Isolation caused by industrialization
C.The outbreak of the smallpox plague
D.The mental stress caused by the Cold War
正确答案：Isolation caused by industrialization