One of the mitigating controls that you wish to rely on is that any increases in credit limits are authorised by the financial controller. The audit assistant checks the company's policy manual and notes that this control procedure is required. He concludes that the control is operating effectively and can be relied on. B. A test of controls of 48 sales transactions was undertaken which resulted in four errors. The working papers noted that none of the errors found was material and the conclusion from conducting the test was that: 'the system is operating satisfactorily. C. Trade payables is a material balance sheet account comprising 20 large and 200 small creditors. Your client presented the audit assistant with a list of creditors making up the balance shown in the trade payables control account in the general ledger. In your absence the audit assistant decided to utilise a judgemental sampling technique to test these creditors. The only procedure the audit assistant used was to randomly select 30 creditors from listing. These were traced to reconciled creditors' statements. D. SIO Pty Limited (SIO) is currently in dispute with the taxation authorities. This year an assessment was issued by the taxation authorities requiring the company to pay an additional $150,000 in taxes. SJO believes that the basis for the assessment was incorrect and inappropriate. Notwithstanding this, it paid the $150,000 to the taxation authorities under protest and lodged a formal objection against the assessment. SIO is carrying forward the $150,000 paid as an 'other receivable' in its year-end financial report. The audit assistant has verified this other receivable by agreeing it to the cash payments books and the bank statement. Required: You are the audit senior and have been presented with the above information by the audit assistant (a new graduate). In each of the above situations, explain why the audit assistant has not obtained sufficient appropriate audit evidence or has concluded incorrectly.