An organic compound A $\left({\mathrm{C}}_4{\mathrm{H}}_{10}\mathrm{O}\right)$ reacts with $\mathrm{HI}$ giving a compound B $\left({\mathrm{C}}_4{\mathrm{H}}_9\mathrm{I}\right)$, which on reduction gives n-butane. On oxidation, 'A' gives a compound C $\left({\mathrm{C}}_4{\mathrm{H}}_8\mathrm{O}\right)$ and then an acid D$\left({\mathrm{C}}_4{\mathrm{H}}_8{\mathrm{O}}_2\right)$.

Deduce the structures of A, B, C and D and mention their IUPAC names.