Which of the following aryl halides cannot give an aryne with $\mathrm{NaNH}{}_2$ in liquid $\mathrm{NH}{}_3$?

Aryne formation needs a hydrogen on a ring carbon adjacent to the carbon bearing the halogen. Both ortho positions of 2-chloro-1,3-dimethylbenzene carry methyl groups and no hydrogen, so elimination cannot occur. The other three halides each have at least one ortho hydrogen.