[单选题]
When an alpha particle isx7v 0 4qx(8q xru/wesl emitted from an unstable nucleus, the a:u8*y7 s1 2gyukbjw0zzw 3 jentomic number of the nucleus 2:bw1njuzk7j8 e 3yg uszy0*w
A. increases by 2.
B. decreases by 2.
C. increases by 4.
D. decreases by 4.
