Step 1: Identifying the Philosophical Statement:
The claim that the development of democracy is the most distinguished contribution of the 20th century is a famous scholarly assessment.
Step 2: Reviewing Amartya Sen's Contributions:
In his work “Democracy as a Universal Value,” Nobel Laureate Amartya Sen argues that while the 20th century witnessed key technology transitions, the rise of democracy as the primary choice of governance was its absolute signature value.
Step 3: Verification:
Lincoln, Gandhi, and Mandela were key political figures in democracy, but Sen made the academic and philosophical conceptualization. Thus, Option (D) is correct.