कौन सा उपकरण उपयोग मुख्य रूप से नहीं होते हुए भी, प्रार्थमिक रूप से प्रकाश की गति मापने के लिए जुड़ा हुआ 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?