In the Cannizzaro reaction given below

$2 \mathrm{ArCHO}\stackrel{{\mathrm{OH}}^{-}}{\to } {\mathrm{ArCH}}_2\mathrm{OH}+{\mathrm{ArCOO}}^{-}$, the slowest step is 

In the given reaction ‘X’ will be :

${\mathrm{C}}_6{\mathrm{H}}_5\mathrm{COCl}\underset{\mathrm{Pd}-{\mathrm{BaSO}}_4,\mathrm{S}}{\overset{{\mathrm{H}}_2}{\to }} \text{'}\mathrm{X}\text{'}$

Methanal + Ammonia$\to$_____.

(A) Borazine
(B) Urotropine
(C) Morphine

Enter your correct answer as A, B or C.