$2-$ There are several compounds with the molecular formula $C_5{H}_{10}B{r}_2.$ Which isomer a$-$d with this formula has the following ${?}^{1}H$ NMR spectrum? $,$ singlet$)$

$5\mathrm{.}3(1H,singlet)$

$3-$ Propose a structure for the following compound.

${?}^{1}H$ NMR spectrum of $C_5{H}_8{O}_2$ :

$1\mathrm{.}90($multiplet$,4$H$)$

$2\mathrm{.}40($triplet$,2H)$

$4\mathrm{.}26($triplet$,2H)$

$3$