Why Has Hoffman's Conclusion That Rationale-Based Induction Is the Most

Why has Hoffman's conclusion that rationale-based induction is the most effective disciplinary technique been criticized?

A) He tested as few as four children in some treatment conditions.
B) He did not compare male and female children.
C) He applied physical discipline to children in some research groups.
D) He was unable to establish a causal link between induction and morality.