During the project, requirements change for a variety of reasons. As needs change and as work proceeds, additional requirements are derived and changes may have to be made to the existing  requirements. It is essential to manage these additions and changes efficiently and effectively. To effectively analyze the impact of the changes, it is necessary that the source of each requirement is known and the rationale for any change is documented. The project manager may,  however, want  to  track appropriate measures  of requirements volatility to judge whether new or revised （ ）are necessary. 
A. proceedings                             
B. controls 
C. forecasting’s                            
D. prelibations