Identify \(B\) and \(D\) in the following sequence of reactions.

\[
\mathrm{CH}_{2}=\mathrm{CH}_{2} \stackrel{\text { Conc. } \mathrm{H}_{2} \mathrm{SO}_{4}}{\longrightarrow} \mathrm{CH}_{3}-\underset{(A)}-\mathrm{CH}_{2}-\mathrm{HSO}_{4}
\]
(addition reaction)
\(\mathrm{CH}_{3}-\mathrm{CH}_{2}-\mathrm{HSO}_{4} \stackrel{\Delta, \mathrm{H}_{2} \mathrm{O}}{\longrightarrow} \mathrm{CH}_{3}-\underset{(B)}{\mathrm{CH}_{2}-\mathrm{OH}}\)
(hydrolysis)
\[
\mathrm{CH}_{3}-\mathrm{CH}_{2}-\mathrm{OH} \stackrel{\mathrm{PBr}_{3}}{\longrightarrow} \mathrm{CH}_{3}\underset{(c)}-\mathrm{CH}_{2}-\mathrm{Br}
\]
(bromination)
\(\mathrm{CH}_{3}-\mathrm{CH}_{2}-\mathrm{Br} \stackrel{\mathrm{Alc} . \mathrm{KOH}(\Delta)}{(\Delta)} \mathrm{CH}_{2}=\mathrm{CH}_{2}\)
(dehydrohalogenation)
Hence, \(B\) and \(D\) in the above given reactions are \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{OH}\) (ethanol) and alc. \(\mathrm{KOH}\).