[单选题]
When an alpha particlp7prq.k0hs6ty9o4nl z 8 2t,xyd1jw ce iif *- .1nf8o2qn qymows emitted from an unstable nucleus, the atomic number of th f-1q2qi.wm* foon 8nye nucleus
A. increases by 2.
B. decreases by 2.
C. increases by 4.
D. decreases by 4.
