[单选题]
The expression (MX - MY - l p 6af-)n:hniMa) x 931.5 rhcjy*xlw (4z. kq 8e5sepresents
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.