[单选题]
The expression (MX - MY -)p07ppum2e *ffv ) xx5 z5tuvs9v( 63 nly yrjov;aj-x Ma) x 931.5 represents
A. the binding energy of the nucleus X.
B. the binding energy of the nucleus Y.
C. the energy released when nucleus X undergoes alpha decay.
D. the energy released when nucleus Y undergoes alpha decay.