Explanation:

- Subramanian Swamy: An economist and politician, known for his involvement in Indian politics and economic discussions, but he has not held any of the three specific positions mentioned.

- P Chidambaram: A well-known Indian politician and lawyer who served as Finance Minister and other ministerial roles, but he never held the positions of Chief Economic Advisor, RBI Governor, or Planning Commission Head.

- Arun Jaitley: A prominent Indian politician and lawyer, known for serving as Finance Minister, but he has never held the roles of Chief Economic Advisor, Governor of RBI, or Planning Commission Head.

- Manmohan Singh: He is the correct answer. He served as the Chief Economic Advisor from 1972 to 1976, the Governor of Reserve Bank of India from 1982 to 1985, and was the head of the Planning Commission as Deputy Chairman from 1985 to 1987.

Correct Answer: Manmohan Singh