In propene, $\mathrm{CH}{}_3-\mathrm{CH}=\mathrm{CH}{}_2$, hyperconjugation takes place through overlap of

1. Athe $\pi$ bond with the $\sigma$ bond of $=\mathrm{CH}{}_2$
2. Bthe $\sigma (\mathrm{C}-\mathrm{H})$ orbital of the $\mathrm{CH}{}_3$ group with the $\pi$ orbital of $\mathrm{C}=\mathrm{C}$
3. Cthe $\sigma (\mathrm{C}-\mathrm{C})$ orbital with an $s{p}^2$ lone pair
4. Dthe $p$ orbitals of the two carbons of $\mathrm{C}=\mathrm{C}$ with each other only