You are the audit manager. You suspected that the company made some sales on special occasions but failed to record them. The sales were made through normal processes and there was no breach of internal control. You asked your assistant how she would go about to find evidence either to prove or disprove your suspicion. She made four proposals, and then she said that she was unsure which one would be the best: (1) confirming accounts receivable; (2) checking payments received after the balance sheet; (3) calculating gross profit ratio; (4) calculating inventory turnover ratio.