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