When ABC Co

When ABC Co. receives a purchase invoice it is checked by the accounts clerk for accuracy then authorised by the line manager who signs it to verify that it has been authorised. How can the auditor test the control over authorisation of invoices is being carried out?

A) Enquire with the accounts clerk to verify that they observe the line manager do this on a regular basis.
B) For a sample of the invoices, re-calculate the invoice amount to ensure it is arithmetically correct.
C) For a sample of invoices ensure that they have been signed by the line manager.
D) For a sample of the invoices verify that the supplier is one of those on the authorised suppliers list.