Which of the following compounds gives a yellow precipitate of iodoform on warming with $\mathrm{I}{}_2$ and $\mathrm{NaOH}$?

The iodoform test needs a $\mathrm{CH}{}_3-\mathrm{CO}{}^{-}$ group (or $\mathrm{CH}{}_3-\mathrm{CH}(\mathrm{OH}){}^{-}$), whose methyl hydrogens are replaced by iodine through the enolate. Pentan-2-one, $\mathrm{CH}{}_3\mathrm{COCH}{}_2\mathrm{CH}{}_2\mathrm{CH}{}_3$, has this group. Pentan-3-one, propanal and benzaldehyde do not.