Relative rate constants (hypothetical, all scaled to $\mathrm{Cl}{}^{-}$ in methanol = 1.0) for $\mathrm{CH}{}_3\mathrm{I}+\mathrm{X}{}^{-}\to \mathrm{CH}{}_3\mathrm{X}+\mathrm{I}{}^{-}$ at 25 ${}^{\circ }$C are: in methanol, $\mathrm{Cl}{}^{-}$ 1.0, $\mathrm{Br}{}^{-}$ 20, $\mathrm{I}{}^{-}$ 90; in DMF, $\mathrm{Cl}{}^{-}$ 4000, $\mathrm{Br}{}^{-}$ 1400, $\mathrm{I}{}^{-}$ 500. Which conclusion follows from these data?

1. ADMF decreases the rate for all three ions, with $\mathrm{Cl}{}^{-}$ affected most
2. BChanging to DMF reverses the order, and $\mathrm{I}{}^{-}$ is accelerated most (about 90-fold)
3. CChanging to DMF leaves the order unchanged and accelerates $\mathrm{I}{}^{-}$ most (about 500-fold)
4. DChanging from methanol to DMF reverses the order of nucleophilicity, and $\mathrm{Cl}{}^{-}$ is accelerated most (about 4000-fold)