Final answer:
The statement that is true of flexible resources is that they are supplied as used and needed.
Step-by-step explanation:
The statement that is true of flexible resources is c. They are supplied as used and needed.
Flexible resources are those that can be adjusted or allocated according to the needs and demands of the business. These resources are not fixed costs, as stated in option a. Additionally, flexible resources can be fully utilized and have no unused capacity, which goes against option b. Finally, the quantity of a flexible resource supplied is not necessarily more than the quantity demanded, so option d is not true either.