[单选题]
The binding energy p v59ug8,c eueyqyzvqlz. 8) 6oer n8l fs/ a9fus3l stm o**qfz6b6ucleon of a $^A_ZX$ nucleus is E. What is the mass defect for the formation of X from its constituent nucleons?
A. $\frac{AE}{c^2}$
B. $\frac{ZE}{c^2}$
C. $\frac{E}{Ac^2}$
D. $\frac{E}{Zc^2}$
