Which of the following statements is correct: O A. Auditors should send negative confirmation to the client's customers if they believe the risk of material misstatement is high for accounts receivable. O B. Auditors can use observation of people's activities as the only source of audit evidence if it is performed in a discreet manner. O C. If the correspondent of a positive confirmation does not respond to an auditor's request, the auditor should perform follow-up procedures. OD. Analytical procedures are only useful at the planning stage of the audit. O E. B and C