A. Product-oriented Approach – Focus on system (or softwarE. quality
B. Process-oriented Approach – Focus on how NFRs can be used in the design process
C. Quantitative Approach – Find measurable scales for the functionality attributes
D. Qualitative Approach – Study various relationships between quality goals

Explanation: Quantitative Approaches in NFRs are used to find measurable scales for the quality attributes like efficiency, flexibility, integrity, usability etc.