Calvin Lee, CPA, performed tests of controls and substantive tests of transactions for sales and collection cycles in an audit of the financial statements for the year ended December 31, 2016. He noted that, possibly due to a change in personnel of the client's accounting department, the test results were not as satisfactory as expected. Discuss how Calvin should react to such test results. A. Calvin needs to do additional substantive testing of sales, sales returns and allowances, write-off of uncollectible accounts and processing cash receipts. B. Calvin needs to determine its cause (whether it is related to the change of personnel) and the implication of the exception on assessed control risk, which may affect the supported detection risk and related remaining substantive tests. C. Calvin needs to reconsider the effect on the confirmation of accounts receivable, including the type of confirmation of accounts receivable, the size of the sample, and the timing of the test. OD. All of the above.