Which one is a nucleophilic substitution reaction among the following?

1. A
   ${\text{CH}}_3\text{CHO}+\text{HCN}\to {\text{CH}}_3\text{CH(OH)CN}$
2. B
   ${\text{CH}}_3-\text{CH}={\text{CH}}_2+{\text{H}}_2\text{O}\stackrel{{\text{H}}^{+}}{\to }{\text{CH}}_3{\text{CH(OH)CH}}_3$
3. C
   $\text{RCHO}+\text{R’MgX}\to \text{Alcohol}$
4. D
   ${\text{CH}}_3{\text{CH}}_2{\text{CH}}_2\text{Br}+{\text{NH}}_3\to {\text{CH}}_3{\text{CH}}_2{\text{CH}}_2{\text{NH}}_2$