Step 1: Understanding the Concept:
The "Open Door Policy" in modern political science usually refers to Deng Xiaoping's economic reforms in China, which opened the country's economy to foreign trade and investment starting in 1978, while the Communist Party kept its political control.
Step 2: Why China fits.
Before 1978, China's economy was closed and centrally planned. Deng Xiaoping's reforms allowed private enterprise, foreign investment, and special economic zones, making China the first major communist country to combine a market economy with one-party rule.
Step 3: Why the other options are wrong.
South Korea and Japan followed export-led growth models but are not associated with the term "Open Door Policy" in this sense. India's economic liberalisation happened later, in 1991, and is called "New Economic Policy" or "LPG reforms" (Liberalisation, Privatisation, Globalisation), not the Open Door Policy.
Final Answer:
China first adopted the Open Door Policy. This corresponds to option (A).