In the Cannizzaro reaction given below $2{\text{C}}_6{\text{H}}_5\text{CHO}\stackrel{O{H}^{-}}{\to }{\text{C}}_6{\text{H}}_5{\text{CH}}_2{\text{OH+C}}_6{\text{H}}_5{\text{COO}}^{-}$   The slowest step is  
 

Attack of OH^- at the carbonyl group

Transfer of hydride ion to the carbonyl group

Abstraction of proton from the carboxylic acid

Protonation of   ${\text{C}}_6{\text{H}}_5{\text{CH}}_2\text{OH}$