साहित्यिक अनुसंधान में निम्नलिखित में से किसे प्राथमिक स्रोत माना जाता है?

The 'Drain of Wealth' theory was propounded by which Indian nationalist leader?

Which event is considered the turning point in Mahatma Gandhi's leadership in the Indian independence movement?

Which African leader is known for his non-violent opposition to colonial rule?