A nucleus $W$ of a radioactive isotope releases a $\beta^{-}$ particle and becomes nucleus $X$. Nucleus $X$ then releases an $\alpha$-particle, producing nucleus $Y$. Nucleus $Y$ releases a $\beta^{-}$ particle and changes into nucleus $Z$. Which statement about $Z$ is correct?
- A$Z$ is a nucleus of a different element from $W$ and has a higher nucleon number.
- B$Z$ is a nucleus of a different element from $W$ and has a lower nucleon number.
- C$Z$ is a nucleus of the same element as $W$ and has a higher nucleon number.
- D$Z$ is a nucleus of the same element as $W$ and has a lower nucleon number.