[单选题]
When a neutron is emith:iq qta+8h o9ted from an unstablkohp)(kp;rxvz.7/ h s0gt wq,e nucleus, the atomic mass number of the nuclkop;. 0, /) vzq(7 xhhktrsgwpeus
A. increases by 1.
B. decreases by 1.
C. does not change.
D. none of the given answers
