Question: Which proposition below is the most powerful refutation of Olivecrona's psychological explanation of law?
A: Coercion plays no part in our decision to obey the law.
B: He provides no empirical evidence in support of his thesis.
C: His argument is itself metaphysical.
D: He neglects the relation between morality and legal duty.
Please eliminate two incorrect options first, then think it step by step and choose the most proper one option.