Which of the following statements about radioactive decay is correct?
- ANeutrinos are always emitted during $\alpha$-decay.
- BThe $\alpha$-particles emitted from a radioactive sample have a continuous range of kinetic energies.
- CThe $\beta^-$ particles emitted from a radioactive sample have a continuous range of kinetic energies.
- DThe proton number of a nucleus decreases by four when it undergoes $\alpha$-decay.