Step 1: Recall the book title.
“Long Walk to Freedom” is the famous autobiography of Nelson Mandela, describing his life journey, his struggle against apartheid, and his years in prison.
Step 2: Check Bharat Ratna connection.
Nelson Mandela was awarded the Bharat Ratna in 1990, becoming one of the few non-Indians to receive it.
Step 3: Eliminate incorrect options.
- Jawaharlal Nehru’s autobiography is “Toward Freedom.”
- S. Radhakrishnan was a philosopher, no such autobiography.
- Khan Abdul Ghaffar Khan’s autobiography is “My Life and Struggle.”
- C. Rajagopalachari did not write “Long Walk to Freedom.”
\[
\boxed{D \text{ Nelson Mandela}}
\]