The correct option is C Culex
Filariasis, commonly called as elephantiasis, is a parasitic infection that causes extreme swelling in the arms and the legs. The disease is caused by a filarial worm, which is transmitted from human to human via female mosquito when it takes a blood meal. Wuchereria bancrofti is one such nematode parasite, that causes filariasis and is transmitted by female Culex.
So, the correct answer is option D.