Which descriptions are correct for a $\gamma$-ray and a $\beta^-$ particle?
- A$\gamma$-ray: high-speed electron; $\beta^-$ particle: electromagnetic radiation
- B$\gamma$-ray: electromagnetic radiation; $\beta^-$ particle: helium-4 nucleus
- C$\gamma$-ray: electromagnetic radiation; $\beta^-$ particle: high-speed electron
- D$\gamma$-ray: high-speed electron; $\beta^-$ particle: helium-4 nucleus