Within a radioactive decay chain, three decays happen one after another, with a particle emitted at each step. The first decay emits a $\beta^-$ particle. The second decay emits an $\alpha$ particle. The third decay emits another $\beta^-$ particle. Nuclides $P$ and $S$ are compared. Which statement is correct?
- A$P$ and $S$ are identical in all respects.
- B$P$ and $S$ are isotopes of the same element.
- C$S$ is a different element of lower atomic number.
- D$S$ is a different element of reduced mass.