[单选题]
When an alpha particle is e+r (;-jaqucv vmitted fromof )g cdnav1 :janp+dset+ x.p1 u8w,- an unstable nucleus, the atomic number of the nucs poawcf apduxd1 g,8j+n-n.e)1 :+v tleus
A. increases by 2.
B. decreases by 2.
C. increases by 4.
D. decreases by 4.
