Answer:
C. Functionality.
Step-by-step explanation:
The main purpose for working on a project and selling as a product is to make it fulfill its function. If a product cannot work the way it was intended to, then it fails to attend the need or luxury it was designed for in the first place.
The product's aesthetic may be important to attract customer interest inside a store before its purchase, but it would remain useless if it cannot function properly.