Consider the above reaction sequence, the Product ‘ C ’ is

In first step bromination reaction will take place. Since hydroxy group on benzene is ortho para directing in nature and aldehyde is meta directing in nature. Bromination will take place at ortho position with respect to hydroxy group and at meta position w.r.t. aldehyde group. 

Next aldehyde will react Hydroxylamine to form oxime. This is an example of nucleophilic addition reaction followed by elimination. In last step dehydration reaction will take place which will convert oxime into cyanide.