To Investigate the Causal Relation Between Corporal Punishment and Aggression

To investigate the causal relation between corporal punishment and aggression, a researcher might consider dividing children into two groups, subjecting one to corporal punishment and the other to verbal admonitions. After a while, the researcher might find it revealing to observe the groups' behavior for signs of aggression, say, in a free-play session. Why has no such study been conducted to date?

A) There is no money available to fund such a project
B) It would be unethical
C) Such a study has not yet occurred to researchers
D) The study would not tell us anything that we don't already know
E) The study is too complicated