Which of the Following Procedures Would Provide the Most Reliable

Which of the following procedures would provide the most reliable audit evidence?

A) Inquiries of the client's internal audit staff held in private.
B) Inspection of prenumbered client purchase orders filed in the vouchers payable department.
C) Analytical procedures performed by the auditor on the entity's trial balance.
D) Inspection of bank statements obtained directly from the client's financial institution.