Explanation

(a)
$\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ O$
||
Only compounds having $–C -$ are reduced to alcohol using $NaBH_{4}$in ethanolic solution.
$\ \ \ \ \ \ \ \ \ O\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ O$
|| ||
$R - C - l,R - C - OH,$
$\ \ \ \ \ \ \ \ \ O\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ O$
|| ||
$R - C - H$ have$- C -$
$\therefore$They are reduced to alcohols by reaction with ethanolic $NaBH_{4}$solution.
O
||
$\therefore R - O - R$ does not have$- C -$ group.
$\therefore$It cannot be reduced to alcohol by alcoholic solution of $NaBH_{4}$.