Step 1: Methyl bromide ($\text{H}_3\text{C-Br}$) reacts with $\text{KCN}$ to undergo nucleophilic substitution ($S_N2$), yielding methyl cyanide or acetonitrile (Compound A) as the major product. Step 2: Acetonitrile ($\text{CH}_3\text{CN}$) on complete acidic hydrolysis ($\text{H}_3\text{O}^+$) gives acetic acid or ethanoic acid (Compound B). Step 3: Acetic acid ($\text{CH}_3\text{COOH}$) is reduced by the strong reducing agent lithium aluminium hydride ($\text{LiAlH}_4$) in the presence of ether to form ethyl alcohol or ethanol (Compound C). Thus, the final product C is ethyl alcohol.