Step 1: Identify the context.
The Indian Planning Commission, active until 2014, was chaired by the Prime Minister of India.
Step 2: Match with the options.
Dr. Manmohan Singh served as Prime Minister and thus chairman of the Planning Commission during his tenure (2004-2014).
Step 3: Eliminate distractors.
(A) Dr. M.S. Ahluwalia - Economist, not chairman.
(B) Dr. C. Rangarajan - Economist, former RBI Governor.
(D) Raminder Singh Gujral - Not a known chairman.
(E) Dr. Subba Rao - Former RBI Governor.
Therefore: The correct answer is (C). \[
\boxed{\text{C}}
\]