In the $\alpha$-particle scattering experiment, a beam of $\alpha$-particles is directed at a thin gold foil. The majority of the $\alpha$-particles pass straight through or are turned through a small angle. Only a very small number are scattered by more than $90^\circ$, so that they appear to bounce back towards the source of the $\alpha$-particles. From this experiment alone, which conclusion about atomic structure cannot be made?
- AMost of the atom is empty space.
- BMost of the mass of an atom is concentrated in the nucleus.
- CThe nucleus contains both protons and neutrons.
- DThe nucleus is charged.