A radioactive nucleus releases an $\alpha$-particle or a $\beta^-$ particle, forming a new product nucleus. Which decay could have produced the product nucleus given?
- A$^{226}_{88}\text{Ra} \xrightarrow{\alpha} \, ^{224}_{86}\text{Rn}$
- B$^{238}_{92}\text{U} \xrightarrow{\alpha} \, ^{242}_{94}\text{Pu}$
- C$^{228}_{88}\text{Ra} \xrightarrow{\beta^-} \, ^{228}_{87}\text{Fr}$
- D$^{231}_{90}\text{Th} \xrightarrow{\beta^-} \, ^{231}_{91}\text{Pa}$