Which of the Following Audit Techniques Would the Auditor Use

Which of the following audit techniques would the auditor use to test the completeness of sales (i.e. ,test whether shipments have been billed to customers) ?

A) trace shipping documents to duplicate sales invoices
B) trace duplicate sales invoices to shipping documents
C) match data file versions of sales invoices to paper records
D) look at subsequent payments after the year end for payments for outstanding invoices