[单选题]
When a neutron is emitted from an unstabltns0u* 3do7+ n 7sryvx1d )vsye nucleus, the atomic mass nu/ds (wg v nx(kpbqe.,i8h (q*imber of the nucleusix(qke*b(gsvhw d,.(n/pi q8
A. increases by 1.
B. decreases by 1.
C. does not change.
D. none of the given answers
