By which of the following sequence of steps can the alcohol $RCH_2CH_2OH (X)$ be converted into $RCH_2CH_2COOH (Y)$?

• A
  $X$ $\xrightarrow{PBr_3}$ $\xrightarrow{KCN}$ $\xrightarrow{H_3O^{+}} Y$
• B
  $X$ $\xrightarrow{PBr_3}$ $\xrightarrow{KCN}$ $\xrightarrow{H_2/Pt} Y$
• C
  $X$ $\xrightarrow{KCN}$ $\xrightarrow{H_3O^{+}} Y$
• D
  $X$ $\xrightarrow{HCN}$ $\xrightarrow{PBr_3}$ $\xrightarrow{H_3O^{+}} Y$