18. Which of the following accounting changes requires an emphasis-of-matter paragraph regarding consistency in the auditors' report?

a. A change in the estimated useful lives of a class of fixed assets. b. A write-off of a patent because future benefits do not appear to exist.

c. A change from the straight-line method of depreciation to an accelerated method.

d. A change in calculating bad debt expense from one percent to two percent of credit sales.