Which statement correctly explains why interstitial carbides such as $\mathrm{WC}$ are harder and have much higher melting points than tungsten metal, while still conducting electricity?

1. AC atoms in the voids add M-C covalent bonding and hinder slip of metal layers, while the delocalised metal electrons are retained
2. Bcarbon forms a molecular lattice with weak van der Waals forces, which raises hardness
3. Ccarbon atoms donate their electrons to tungsten, which removes all free electrons
4. Dthe metal lattice is destroyed and replaced by a discrete ionic lattice of $\mathrm{W}{}^{4+}$ and $\mathrm{C}{}^{4-}$