What Explains the Relationship Between Social Class and Mental Illness

What explains the relationship between social class and mental illness?

A) Greater social stress associated with lower-class life may cause mental illness.
B) The onset of mental illness may cause people to lose their jobs and move downwards in the social classes.
C) Sociologists disagree as to whether lower-class life causes mental illness or the onset of mental illness causes people to move down in social class.
D) There is no relationship between social class and mental illness.