[单选题]
The expression (MX -5 uhx/ ebb gl*s-5jka9 MY - Ma) x 75y 0w vul)i5jckqqo a(bq:,u931.5 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.