Research Suggests That There Exists a Relationship Between Corporal Punishment

Research suggests that there exists a relationship between corporal punishment and low self-esteem, delinquency, aggressiveness, depression, and other problems, however this research has several limitations. What is the limitation of this research from the perspective of longitudinal research?

A) Longitudinal research says this research limited because we have no way of knowing if physical punishment "caused" the behavioural problems in some of the adolescents and adults who report having been spanked as children.
B) Longitudinal research says that this research fails to differentiate harsh from mild corporal punishment.
C) Longitudinal research states that this research is flawed because it does not consider the possibility that parents who rely on corporal punishment and have difficult children who grow up to exhibit problems share a negative genetic background with their children.
D) Longitudinal research says that this research is limited because it does not inquire about the remainder of the parents' socialization practices.
E) Longitudinal research says this research is limited because punishment has not been adequately conceptualized.