An atomic nucleus releases a $\beta$-particle. How does this affect the proton number and the nucleon number of the nucleus?
- Aproton number $-1$, nucleon number $+1$
- Bproton number $0$, nucleon number $-1$
- Cproton number $+1$, nucleon number $-1$
- Dproton number $+1$, nucleon number $0$