Refactoring, as it applies to the practice of extreme Programming (XP), refers to:
A . Restructuring the estimate by applying a higher cost performance index during ¡°what if¡± analysis.
B . Modifying the project due to scope changes, resource availability, and cost and schedule variances.
C . Modifying the cost baseline due to an increased estimate at completion and a negative cost variance.
D . Restructuring of code so as to improve the code without changing its external behavior.