Which of the following is the commonest cause of malaria in the world?

Malaria has a worldwide distribution between 45degN and 40degS latitude, generally at altitudes below 1800 m. P vivax is the most widely distributed of the four species, and together with the uncommon P malariae, is found primarily in temperate and subtropical areas. P falciparum is the dominant organism of the tropics. P ovale is rare and found principally in Africa. Ref: Ray C.G., Ryan K.J. (2010). Chapter 50. Sporozoa. In C.G. Ray, K.J. Ryan (Eds), Sherris Medical Microbiology, 5e.