Which of the following compound forms red precipitate when treated with Fehling's solution ?

$\mathrm{RCH}_{2} \mathrm{X}$

$\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{OH}$

$\mathrm{RCH}_{2} \mathrm{CHO}$

$\mathrm{RCOOH}$