In 2003 and 2004, an auditor found that approximately 4 percent of processed sales invoices were not mathematically accurate. In late 2004, the client implemented a control requiring that all sales invoices be extended by two independent employees. When planning the 2005 engagement, the auditor estimated a 4 percent error rate for processed sales orders. This is an example of which heuristic?

a. Availability.

b. Anchoring and adjustment.

c. Representativeness.

d. Base rate neglect.