Explanation:

- Kala-azar, also known as visceral leishmaniasis, is a disease caused by protozoan parasites.

- These parasites belong to the genus *Leishmania*, with *Leishmania donovani* being the most common culprit.

- The disease spreads through the bite of infected female sandflies.

- Option 1 - Bacteria: Bacteria cause diseases like tuberculosis and strep throat, but not kala-azar.

- Option 3 - Fungi: Fungal infections include athlete's foot and ringworm, but not kala-azar.

- Option 4 - Viruses: Viruses cause diseases like the flu and COVID-19, but not kala-azar.

Correct Answer: Option 2 - Protozoa: Kala-azar is caused by protozoa. Your answer is right.