The correct option is D All of the above.
Dehydrohalogenation involves removal of (elimination of) a hydrogen halide by abstracting β−H from a substrate in presence of base (alc. KOH) to form alkenes.
Since, removal of β hydrogen takes place in elimination step thus it's a β elimination reaction.
CH3−CH3|C|CH3−Xalc.KOH−−−−−→CH3−C|CH3=CH2+H2O+KX