The business managers had clearly stated that the delivered website must simultaneously accommodate millions of...

Nonfunctional requirements are the characteristics or qualities of a solution that describe how well it performs or operates. They include aspects such as usability, reliability, availability, scalability, security, performance, etc. The website crashing frequently indicates that the nonfunctional requirements related to availability and performance were not identified and tested properly. Quality attributes are another term for nonfunctional requirements, so option A is equivalent to option C. Critical business requirements and essential product requirements are both functional requirements, which describe what a solution does or provides, not how well it does it. Therefore, options B and D are incorrect. References: PMI Professional in Business Analysis (PMI-PBA)® Examination Content Outline, page 18; Business Analysis for Practitioners: A Practice Guide, page 114-115.