What is "validation" with respect to the engineering design process?

a$.$ The process of basing a design on its use and design space environments.

b$.$ The process of starting the design with an ill$-$defined problem

c$.$ The process of ensuring that design solutions meet the clients' requirements and other stated design specifications.

d$.$ The process of ensuring that delivered entities meet the users' needs.

e$.$ The process of identifying the general problem as well as who or what is affected.