$9$ The substantive analytical procedure known as trend analysis is best described by

a$.$ The comparison, across time or to a benchmark, of relationships between financial statement accounts or between an account and nonfinancial data.

b$.$ Development of a model to form an expectation using financial data, nonfinancial data, or both to test account balances or changes in account balances between accounting periods.

c$.$ The examination of changes in an account over time.

d$.$ The calculation of days sales outstanding and comparing the value to the industry average.