Consider (i) $\mathrm{CH}{}_3\mathrm{Br}+\mathrm{I}{}^{-}\to \mathrm{CH}{}_3\mathrm{I}+\mathrm{Br}{}^{-}$ (single-step ${\mathrm{S}}_{\mathrm{N}}2$) and (ii) $(\mathrm{CH}{}_3){}_3\mathrm{CBr}+\mathrm{Cl}{}^{-}\to (\mathrm{CH}{}_3){}_3\mathrm{CCl}+\mathrm{Br}{}^{-}$ by an ${\mathrm{S}}_{\mathrm{N}}1$ path in two steps (ionisation, then capture of the carbocation by $\mathrm{Cl}{}^{-}$). Counting both reactions together, the number of transition states and of reactive intermediates is

1. A3 transition states and 1 intermediate
2. B4 transition states and 1 intermediate
3. C2 transition states and 1 intermediate
4. D3 transition states and 2 intermediates