Identity the compound 'D' in the following series of reactions.
$CH_{3}-CH_{2}-Br \overset{alc. KOH}{\rightarrow} 'A' \overset{Cl_{2}/CCI_{4}}{\rightarrow} 'B' \overset{NaNH_{2}}{\rightarrow} 'C' \xrightarrow[1percentHgSO4]{40percentH2SO4} 'D'$