A nucleus of a radioactive element emits an $\alpha$-particle, then a $\beta^-$ particle, and afterwards another $\beta^-$ particle. Which statement gives the description of the final element produced?
- AIt is a different element of higher proton number than the original element.
- BIt is a different element of lower nucleon number than the original element.
- CIt is an isotope of the original element.
- DIt is the same element as the original element but with a different proton number.