Choice "A" is correct. Restricting access to the computer center by use of biometric devices represents a general control. General controls are designed to ensure that an organization's control environment is stable and well managed. Choice "d" is incorrect. Limiting entry of sales transaction to only valid credit customers likely represents an application control (imbedded within the software). Application controls prevent, detect and correct transaction errors and fraud and are application specific.Choice "b" is incorrect. Creating hash totals from Social Security numbers for the weekly payroll is a processing control. Processing controls include recalculation of batch totals and similar procedures.Choice "c" is incorrect. Restricting entry of accounts payable to only authorized users represents a user control.