Functional design involves reliability, maintainability, and usability perceptual maps reverse engineering a feasibility study

Functional design is the design that describes how the product will perform. 
During the functional design three performance characteristics are considered. It involves reliability (the probability that a product will perform its intended function for a specified period of time), maintainability (the ease with which a product is maintained or repaired) and usability (the ease of use of a product or service).

The correct answer would be b