Explanation:

- Radcliffe-Brown was a prominent British social anthropologist, known for his work on the Andaman Islanders and structural functionalism, not specifically on the Yako tribe.

- E.R. Leach was famous for his studies in Burma and Sri Lanka, not for research on Nigerian tribes.

- Evans-Pritchard mostly focused on the Azande and Nuer people in Sudan.

- D. Forde (Daryll Forde) is best known for his ethnographic study of the Yako (Yakö) tribe in Nigeria. He made significant contributions to the understanding of social structure and agriculture among the Yako.

Option 4 – D. Forde is the correct answer.