Activities that do not add value to a product or service that customers are willing to pay for are considered to be:

A) a constraint.
B) part of the overhead costs of a business.
C) normal business activities.
D) non-value-added activities.

Non-value-added activities are those that do not add value to a product or service that customers are willing to pay for. These activities are typically considered wasteful and should be eliminated or minimized in order to improve efficiency and reduce costs. Examples of non-value-added activities include excess inventory, overproduction, and unnecessary transportation.