[单选题]
When a neutron is emitted from an unstable nucleuszjk0al,,n ve), the atomic mass num84wsz.s at.z d2np /(b.hd igmber of the nuhat( pwdi.4 g ./28szsd zn.bmcleus
A. increases by 1.
B. decreases by 1.
C. does not change.
D. none of the given answers