A graph plotted with neutron number on the vertical axis and proton number on the horizontal axis shows a chain of radioactive decays. Nucleus $X$ is the initial nucleus in the chain and, after the decays are complete, nucleus $Y$ is produced. What is emitted in the chain of decays?
- Aone $\alpha$-particle followed by one $\beta$-particle
- Bone $\alpha$-particle followed by two $\beta$-particles
- Ctwo $\alpha$-particles followed by two $\beta$-particles
- Dtwo $\beta$-particles followed by one $\alpha$-particle