The cost of testing incoming materials received from suppliers would be classified as a(n) :

A) prevention cost.
B) appraisal cost.
C) internal failure cost.
D) external failure cost.

The cost of testing incoming materials received from suppliers falls under the category of appraisal cost. This is because these costs are incurred to ensure that purchased materials meet specific quality requirements before they are used in the manufacturing process. Appraisal costs are associated with activities that are designed to detect defects or non-conformance to quality standards, and they help in identifying and correcting quality problems before they result in product defects or failures.