The carrier of Kala-azar, also known as visceral leishmaniasis, is primarily the (a) Anopheles mosquito. This vector transmits the parasitic protozoa Leishmania donovani, responsible for the disease. When an infected Anopheles mosquito bites a human, it injects the Leishmania parasites into the bloodstream, leading to infection. Unlike the Culex mosquito (b), which is associated with diseases such as West Nile virus, and the C.C. fly (c), implicated in transmitting sleeping sickness, the Anopheles mosquito is the specific vector for Kala-azar transmission. The Cicata fly (d) is not known to transmit Kala-azar or any similar disease.