केसवानंद भारती मामले में मुख्य रूप से किस संवैधानिक संशोधन अधिनियम की वैधता को चुनौती दी गई थी, जिसके कारण मूल संरचना के सिद्धांत का विकास हुआ?

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?