Which of the Following Is Ordinarily Considered an Extended Procedure

Which of the following is ordinarily considered an extended procedure during the independent audit of financial statements?

A) Sending positive confirmations on recorded customer accounts receivable balances.
B) Performing physical observation and test count during the client's inventory taking.
C) Measuring the time lag between the date of recording cash receipts in the books to the date of the deposit credit in the bank.
D) Conducting interviews with the client's sales billing personnel to learn about sales recording control activities.