I need more explanation about why options are correct or wrong.

1 )Which of the following statements relating to control activities employed in the sales cycle ismost correct?

A.To addresscompletenessfor sales revenue, the client should check that all pre-numbered shipping documents are accounted for and reflected in an invoice issued to a customer, with all exceptions followed up.

B.To addresscompletenessfor sales revenue, before issuing an invoice, the client should check that he details on the invoice are reconciled to a customer purchase order and shipping documents, and follow up all exceptions.

2) Which of the following statements relating to sampling when performing tests of controls ismost correct?

C.Systematic selection is an appropriate non-statistical sampling approach for testing controls.

D.Statistical sampling eliminates sampling risk.