Why Was the Payroll Office, Once a Constant Feature of HR

Why was the payroll office, once a constant feature of HR departments, was removed from HR?

A) Payroll became too much work for the human resource staff.
B) Human resources lost a political struggle with the finance department for the control of the payroll activity.
C) It was seen as more efficient to have payroll done by an outside service.
D) The most applicable knowledge and expertise became centered in activities having to do with accounting and finance.