A small amount of $\mathrm{NaI}$ is added to a mixture of 1-chlorobutane in aqueous acetone, in which 1-chlorobutane hydrolyses only slowly. The hydrolysis becomes much faster. Select the correct statements.

1. AIodide acts as a catalyst because it is a poorer leaving group than chloride.
2. B1-Iodobutane is attacked by water far more easily than 1-chlorobutane because iodide is a better leaving group.
3. CIodide is regenerated in the second step, so only a catalytic amount is needed.
4. DIodide is a much better nucleophile than water and displaces chloride by SN2 to give 1-iodobutane.