For each of the following independent situations: (a) identify the most relevant control activity, (b) identify the most relevant general audit objective(s) for the control activity, (c) design an appropriate test of control for the control activity, (d) choose one of the general audit objectives identified in (b) and design an appropriate substantive test for it.

Please note: Choose a substantive test that produces reliable evidence.Do not use analytical procedures unless an accounting estimate is involved.Do not use audit procedures that produce unreliable evidence.

1. Sales invoices are pre-numbered.
2. Before a sales invoice is sent to a customer, a second employee is required to double check the price, quantity and total value of sales for the transaction.
3. Changes to the audit client's list of acceptable suppliers must be approved by the Chief Financial Officer.
4. Petty cash and cheque books are locked in a safe after business hours.