(Pelican : Reptile) , (Gnu : Antelope) , (Elk : Deer) , (Shark : Fish)
Option:
Justification: In all other pairs, first is a type of the second.

(Pelican : Reptile) , (Gnu : Antelope) , (Elk : Deer) , (Shark : Fish)
Justification: In all other pairs, first is a type of the second.