Which of the following audit procedures for obtaining audit evidence is correctly describe

Which of the following audit procedures for obtaining audit evidence is correctly described？

A.Recalculation involves the auditor’s independent execution of procedures or controls which were originally performed as part of the entity’s internal control

B.Confirmation consists of seeking information of knowledgeable persons, within the company or outside the company

C.Reperformance consists of checking the mathematical accuracy of documents or records

D.Observation consists of looking at a procedure or process being performed by others

请帮忙给出正确答案和分析，谢谢！