Reaction of phenol with chloroform in presence of dilute sodium hydroxide finally introduces which one of the following functional groups?

This is the Reimer-Tiemann reaction. Phenol reacts with ${\text{CHCl}}_3$ and $\text{NaOH}$ to form salicylaldehyde. The reaction introduces an aldehyde ($-\text{CHO}$) group at the ortho position of the benzene ring.