Final Answer:
After building a prototype, conducting rigorous functional testing to assess performance and safety qualifications is part of the c) product development phase in the new-product development process.
Step-by-step explanation:
The new-product development process involves several phases, and in this scenario, the relevant phase is product development (Option C). After creating a prototype, the focus shifts to testing and refining the product to ensure it meets performance and safety standards. This phase involves comprehensive functional testing to assess the product's capabilities and reliability.
Option A (product design) typically precedes the prototype stage, while options B (screening), D (concept testing), and E (test marketing) are associated with earlier stages of the new-product development process, involving idea generation, evaluation, and initial market testing.
Option C is the answer.