Which of the Following Is Not a Type/category of Control

Which of the following is not a type/category of control activities?

A) Adequate separation of duties (useful for making sure that individuals who authorize transactions are different from those who execute them)
B) Adequate documents and records (documents and records are the physical objects by which transactions are entered and summarized and can be the audit trail by which auditors can investigate wrongdoings)
C) Proper authorization of transactions and activities (most common controls in e-business include passwords, firewalls, digital signatures, and biometrics)
D) Use of internal auditors